The following points highlight the top twenty classical microscopists (1635-1922) with its contribution and influences. The classical microscopists are: 1. Robert Hooke (1635-1703) 2. Leeuwenhoek (1632-1723) 3. Swammerdam (1637-1680) 4. Malpighi (1628-1694) 5. Linnaeus (1707-1778) 6. Lyonet (1707-1789) 7. Ehrenberg (1795-1876) 8. Cuvier (1769-1832) 9. Owen (1804-92) 10. Bichat (1771-1801) 11. Lamarck (1744-1829).
Classical Microscopists # 1. Robert Hooke (1635-1703):
Of all the classical microscopists, Robert Hooke was unquestionably the most brilliant. He was very sickly from his childhood and his ill health prevented him from receiving a normal education. He, however, received a good scientific training of the University of Cambridge. After the foundation of the Royal Society he entered its service as a salaried ‘curator of instruments’.
Hooke was primarily a physical experimenter and most of his best work lie outside the domain of biology. He gave his attention to microscopic studies for some time and published his work in his book ‘Micrographia’ published in London in 1665.
The book opens with a description and figure of the microscope he used. In his figure of the microscopic structure of the cork he has designated the walls as “cell”. The word cell is still alive in modern biology. He has depicted a polyzoon for the first time.
The markings on the scales of fishes, the structure of the sting of the bee, the radulae of molluscs, foot of the fly and structure of the feathers are some of the instances of his microscopic observations.
He lacked fixedness of purpose in the proper employment of his talents. His pioneering work in micros- copy gave a powerful stimulus to microscopic studies in England and systematic studies with microscope became escalated.
Classical Microscopists # 2. Leeuwenhoek (1632-1723):
Leeuwenhoek was born in 1632 at Delft. He came of a wealthy brewers’ family. His schooling came to an end at the age of sixteen and he never learnt any language but his own Dutch. He was sent to Amsterdam to join a clothing business as boo-keeper and cashier. But he never lied the appointment and came back to Delft where he owned a draper’s shop and pent all his spare time on microscopoy.
Leeuwenhoek (Fig. 6.10) used to send his communications to the Royal Society. These were published by the society in English or in Latin translations from the original Dutch. He turned his microscope in all directions—to the minerals as well as to the animal and vegetable kingdoms.
He observed the minute circulation of blood and demonstrated the presence of capillaries (Fig. 6.11) between arteries and veins and thus completed the chain of observations which began with Harvey. He followed this by descriptions of blood corpuscles.
His observations that blood corpuscles of fish and frog are oval and that of man is round are correct. He also made descriptions of the blood corpuscles of some invertebrates. He gave excellent account of muscles, the lens of eye, teeth, skin and many others.
Leeuwenhoek’s work on the compound eyes of insects are remarkable. He showed that these lenses form numerous inverted images and the insects are endowed with the power of quickness of sight. Other worth mentioning observations of Leeuwenhoek are the development of ant, poison and spinning apparatus of spiders and the life history of Aphids. Parthenogenetical development of Aphids was recorded by him.
Leeuwenhoek focused his attention to the world of the unseen too. His papers on minute fresh water creatures like Rotifers, Hydra and Volvox were the first of their types. His remarkable achievement is that he could catch a glimpse of bacteria.
Leeuwenhoek impressed his contemporaries most. He led an easy and prosperous life and showed an avidity amounting to passion towards the microscope. He gave good descriptions and drawings of his instruments. He was much balanced and had a good power for observation. But he was never a solver of problems.
Classical Microscopists # 3. Swammerdam (1637-1680):
Swammerdam (Fig. 6.12) was born in 1637. His father had a taste for collection and thus “from the earliest dawn of his understanding young Swammerdam was surrounded by zoological specimens”. He thus became passionately devoted to the study of natural history.
His father wanted that he should go to the church. But he had no taste for theology. At the age of twenty-six he entered the University of Leyden. He went to Paris and took his degree of Doctor of Medicine in 1667.
His work were collected in a book entitled “Biblia Naturae”‘, that was published fifty-seven years after his death. The book contains about a dozen of life histories of insects. Of these, the Mayfly (Ephimera) is the most famous and that one on Honey bee the most elaborate.
The greater amount of his work deals with structural Entomology (Fig. 6.13). His other work include the fine anatomy of the snail, structure of the clam and squid, development of frog and observations on the contraction of muscles.
After graduating in medicine, he never did practice but devoted his time in examining minute anatomy. He was a skilful and judicious experimenter. His work on respiratory processes and his demonstration that muscles though alter in form but do not alter in size when they contract was a new idea. He improved the technique of injection. His work did a lot to advance physiological knowledge.
Classical Microscopists # 4. Malpighi (1628-1694):
Malpighi was born in 1628 near Bologona. He came of an affluent peasant family and under the patronage of his parents had a good schooling. He soon developed a taste for belles-letters and philosophy. At the age of twenty-three, for a profession, he started studying medicine and obtained the degree of Doctor of Medicine in 1653 from the University of Bologona.
In 1656 he got a post there and started his career as a teacher and investigator. Later he joined the University of Pisa and after three years again came back to Bologona University.
Malpighi (Fig. 6.14) remained always busy with experiments and research. He made a number of important observations which advanced the knowledge of biology to a great extent.
He first demonstrated the structures of lungs and showed the presence of air cells in it. He presented a tolerable idea of how the air and blood are brought together in lungs. He extended the work of Harvey and demonstrated the presence of capillary system in the lungs of toad. He also demonstrated the mucous layer or ‘pigment layer of the skin’.
Malpighi extended the work of Fabricius on the development of chick. With the aid of his microscope he observed that during the early stages of development of the chick a series of vessels arises from the aorta as it leaves the heart. He was, however, unaware of the nature and meaning of these vessels.
The most striking Malpighi’s research is the monograph on the anatomy of silk moth (Fig. 6.15). The monograph was the first of its kind in the history of Zoology. Malpighi was the first to observe the tracheae and spiracles of the insect body and could arrive at a correct conclusion about their function.
He also did many work on plant anatomy.
Malpighi influenced his contemporary world to a great extent. He was honoured at home and abroad. In 1667, the Royal Society requested him to send his communications to them. Most of his work were published in London under the auspices of the society.
His Latin style was, however, not good and contained many vague and obscure theoretical explanations. His work show that he was neither apt at designing experiments nor was he a skillful interpreter of his results. As an observer, however, he has seldom been equalled.
Classical Microscopists # 5. Linnaeus (1707-1778):
The great Swedish naturalist, Linnaeus or Lirine was born in Rashult in 1707. His father was a poor clergyman. His father’s resources were limited and he was persuaded to send his son to Lund and afterwards to Upsala to become a student of medicine. Linnaeus showed little interest in stereotyped instructions.
He spent his time in collecting natural history specimens. His father became very upset at the report of his son’s low scholarship. He was about to arrange for an apprenticeship for Linne to a shoemaker. He, however, was prevented in doing so and Linne was allowed to continue.
In 1732, Royal Society of Upsala wanted to send him to Lapland as a collector and observer. He immediately accepted the offer and went out to Lapland for the excursion without completing his studies. On returning to Upsala he fell into financial distress. At this stage he was helped by his fiancee and obtained the degree of doctor of medicine from the University of Hardewyk in 1735.
On his return to Sweden he was appointed Professor of Natural History at Upsala.
Linnaeus (Fig. 6.16) had a passion for classification. Not only did he classify plants and animals but also the minerals and even diseases. He introduced the system of Binomial nomenclature of plants and animals. He assigned to every known plant and animal a place in his system.
This involved placing it first in a class, then in an order, then in a genus, then in a species. His great work are Systema Naturae (1735), Genera plantarum (1737), Foundamenta Botanica (1735) and Biblio- theca Botanica (1736).
Linnean system of classification contained the following classes—Mammals, Birds, Reptiles, Fishes, Insects and Vermes. The first four classes had already been grouped together by Aristotle. The remaining classes of Insects and Vermes contained all the groups of animals without vertebrae. Here he was behind Aristotle. Linnean arrangement of Animal Kingdom is given below.
Heart with 1 or 2 ventricles and 2 atria.
Blood red and warm:
Heart with 1 ventricle and 1 or 2 atria.
Blood red and cold:
3. Breathing by lungs—Reptiles.
4. Breathing by gills—Fishes.
Heart with 1 ventricle and no atria.
Blood colourless and cold:
5. With antenna—Insects.
6. With tentacles—Vermes.
The work of Linnaeus marked a lasting influence on natural history. He brought into use the method of and means of naming animals and plants. The method is §till in practice. The Systema Naturae is not merely a treatise on the structure of animals and plants, it is a catalogue of the productions of nature arranged most methodically.
The second important feature of his work is that they were done with much labour, extreme brevity and great clearness.
Despite his industry and force, Linnaeus gave natural history a one sided development and many disciplines of biosciences were given little attention. His students like their teachers became collectors and classifiers.
“Thus in the zeal for naming and classifying, the higher goal of investigation, knowledge of the nature of animals and plants was lost sight of and the interest in anatomy, physiology and embryology lagged”.
The general idea of Linnaeus concerning the nature of species was wrong. He held that species are constant and invariable. “There are as many species as they were created in the beginning” said Linnaeus. Such a concept contradicted many naturalists and consideration about the origin of species became burning question.
Classical Microscopists # 6. Lyonet (1707-1789):
Lyonet was born in the Hague in 1707. He had a good education and by profession he was a lawyer. His talents were great and varied. He was at the same time a painter, a sculpture, an engraver and a very gifted linguist with skill in eight languages.
Lyonet (Fig. 6.17) had no training in anatomy but he had a flare for dissection. His interest in the subject was culminated in the publication of his treatise on minute anatomy of insects (Fig. 6.18). His monograph (1750) on the caterpillar of the goat moth displayed not only patience but great skill as dissector and sketch maker.
He engraved his own figures on copper. He worked out in details the layers of muscles and could distinguish 4,041 separate muscles. As an artist he helped many naturalists by making drawings for them. He drew the figures for Lesser’s Theology of Insects (1742) and for Trembley’s famous treatise on Hydra (1744).
The extraordinary details shown in the drawings of Lyonet created a sensation. The existence of such complicated structures within the body of so small an insect was discredited. Some of the critics opined that even if such structures exist they should be beyond the resolution power of human eye.
The work of Lyonet on minute anatomy might have induced other scientists following him to go for more minute things in the organisation of living system.
Classical Microscopists # 7. Ehrenberg (1795-1876):
Ehrenberg (Fig. 6.19) was a German naturalist who held the chair of medicine in the University of Berlin. He was a great scientific traveller who attained great scientific height.
He was one of the early observers of nerve fibres. His book “The Infusoria as Perfect Organisms” is a hall mark in the study of Protozoa. As Ehrenberg had a best microscope of his days at his disposal he could investigate upon minute animals. He made a faithful representation of the habit, feeding and discharging of undigested food of these protozoa.
Ehrenberg was the first to demonstrate the existence of fossil forms of protozoa. His “Mikrogeologie” (1854) was for many years the standard reference work in this line. He also demonstrated that marine phosphorescence is due to the protozoa, Noctiluca.
Leeuwenhoek left little unnoticed of the microscopic world and it was he who made first records of unicellular animals. From his time onward these animals became favourite objects of microscopic studies. The first standard work in this line was done by Miiller in 1786. Ehrenberg further extended the domain of these animalcules in the minds of biologists.
Ehrenberg was, however, wrong in his interpretation of the nature of these organisms. He believed in the presence of many organs within the organism. His publication was almost simultaneous with the announcement of the cell-theory (1838-39). The wide acceptance of the theory overthrew his conception of protozoa.
The protozoa are the simplest expressions of life and afford a fertile field for experimentation. A separate division of biological study called “Protozoology” is now in operation. The germ of the subject was kindled by Ehrenberg.
Classical Microscopists # 8. Cuvier (1769-1832):
Cuvier was the son of a Swiss Protestant officer in the French army. He was born near Belfort in 1769. He studied and in 1795 became an assistant- at the Musee d’ Histoire Naturelle at Paris. He was selected by Napoleon to direct the reform of education in France.
All work of Cuvier (Fig. 6.20) are guided by the “principle of correlation of parts”. According to him organs do not function in nature as separate entities but they are certainly the parts of organic living wholes. In these living wholes there exists certain relation of parts which are fundamental to their modes of life. Thus feathers are always found in birds and not in other animals.
Presence of feathers is related to certain formation of the forelimb so that it may be used as a wing. The forelimb is related to collarbone, collar-bone to chest and so on. He studied the fossils of elephants, mammals and many reptiles. His inferences on fossils were not correct.
He believed in fixity of species. That is there is no evolution and there had been a succession of animal populations. He believed that the vast number of species, many no longer existing, had appeared on earth at different periods following catastrophes.
He developed considerable interest in the history of the development of sciences. He wrote a number of volumes on the rise of natural science. His historical writing can still be consulted with profit.
Cuvier has been called the “Dictator of Biology”. He enjoyed a commanding position and was admitted as leader of science for years. He was a favourite of Napoleon Bonaparte and held the post of Director of the Higher Centres of Learning in France. But whatever prominence he attained in the Government he never lost his love for natural science.
Cuvier is best known by his book ‘Le Regne Animal……… ‘ which was published in 1817. It was the most comprehensive biological work since Linnaeus. It was the product of 25 years research. The work describes a species from every genus then recognised with illustrations. The system of classification divided animals into four great embranchments. Each embranchment was built on its own peculiar and definite plan.
The major embranchments are:
1. Vertebrata—animals with back bone.
2. Mollusca—slugs, oysters, snails, etc.
3. Articulata—jointed animals as insects, lobsters, spiders.
4. Radiata—all remaining animals.
From 1801 to 1805 appeared his “….. Anatomie Comparee”, a systematic treatise on the comparative anatomy of animals belonging to vertebrates and invertebrates.
He was interested on fossils and wrote a book in 1812 on the fossils about Paris, which laid the foundation stone of vertebrate palaeontology. He studied through his own industry to become an independent observer. He was certainly the founder of comparative anatomy.
His influence was stimulating to research. He had encyclopedic knowledge and profound energy. He formed vast scientific schemes and brought many of them to fruition. He had the gift of inspiring others and of causing them to work for him. Thus he formed a good team work.
A critical analysis of his work will show that he was often inaccurate in finer details of his subject. On the whole- his intellectual leadership paved the way for further development of certain branches of Biology and his faults and adherence to a number of ideas retarded the progress of certain branches.
Classical Microscopists # 9. Owen (1804-92):
Owen was an English Biologist and was born in 1804 at Lancastar. He began his career as a surgeon’s apprentice and then studied medicine at Edinburgh. In 1827 he became an assistant at the Hunterian Museum. Later he became director of the Natural History department of the British Museum. It was a place with immense wealth of material and Owen came up to the occasion in utilizing them.
Owen (Fig. 6.21) was tremendously influenced by Cuvier. Most of his work were published in the Scientific proceedings of the Zoological Society of London. His “Memoir on the pearly Nautilus” (1532) was his first significant contribution. Owen dissected a large number of animals.
The dissection of rare animals like monotremata, marsupialia was recorded in “Catalogue of the physiological series of comparative anatomy contained in the Royal College” as his monumental work. It is still of great value.
The credit of introducing the concept of ‘Analogy’ and ‘Homology’ in Anatomy goes to Owen.
Owen was one of the admitted masters of Palaeontology. He did immense investigations on the fossilised teeth of mammals. He wrote many monographs on extinct animals. Amongst these, the best known ones are on the extinct bird Dinornis of New-Zealand and on the giant extinct sloth Mylodon of South America (Fig. 6.22).
He discovered the parasite Tnchinella spiralis which causes the disease Trichinosis.
Owen was a prolific writer. He was singular in most of his thoughts and many of his generalizations could not stand the trial of time. His work on Palaeontology- was creditable.
He could lay stress on the fact that there lies an alliance of comparative studies with the doctrine of evolution and in seeking such an alliance attention should be focused on structure and not on function. He, however, was an obstinate opponent of Darwinian concept of evolution.
Classical Microscopists # 10. Bichat (1771-1801):
Bichat (Fig. 6.23) was born in 1771 and died a premature death at the age of thirty-one. His father was a physician. Bichat showed brilliance from his early student days. He was distinguished in Latin and mathematics and showed inclination to natural history from his early life. He went to Lyons to study medicine.
The turbulent events of the French revolution forced him to go to Paris from Lyons. He got a good training in Paris. He be came the Professor of Anatomy at the age of twenty-six.
He had a brief span of .life. His industry was phenomenal. It is said that in a single winter he examined with care as many as six hundred bodies in pursuance of his research on pathological anatomy. His treatises on the membranes, the phenomena of life and death and General Anatomy show the intensity and completeness of his investigations.
Bichat supplemented Cuvier and at the same time carried the organisation of animals to a deeper level. Bichat made intensive studies of tissues that make up organs. This particular branch is now called Histology. Thus he is called the father of Histology.
He undoubtedly has drawn the attention of the world to the minute structure of the tissues within a productive period of seven years. He has published such work that has created an epoch and has laid an everlasting impression on the history of Biology.
Classical Microscopists # 11. Lamarck (1744-1829):
Jean Baptiste de Monet Lamarck (Fig. 6.24) was born in 1744 at Bazantin. As his father wished him to enter priesthood, he was sent to the Jesuit College at Amiens. As soon as his father died he left the college to join the French army then engaged against the Germans in the seven years war.
One of his comrades caused injury to the glands of his neck by lifting him by the head. This made him unfit for military life and he left the military service. Lamarck went to Paris to study medicine supporting himself with clerical work.
He found special interest in Botany and abandoned the thoughts of a medical career. At the age of fifty he was forced to take a chair in Invertebrate Zoology in the Mliseum d Historire Naturelle. Though he had no training in Zoology at the time of his appointment, he took it as a challenge and mastered the subject. He devoted the rest of his life to Zoology.
Lamarck had a struggling life through- Out. He had to fight against poverty and against his contemporaries who never could encourage or recognise his talents. Lamarck died in 1829 having been blind totally for ten years.
Lamarck’s first biological work was on the flora of France. He was founder of the term ‘Biology’. He believed that the animal and plant series, must at some remote point, were continuous with each other. He was of the opinion that living things should be studied as an entire entity—an attitude to which he was helped by his knowledge both in Botany and Zoology.
Lamarck’s work on classification is probably his best. He separated spiders and crustaceans from insects. The class ‘Vermes’ created by Linnaeus was rather loose. Lamarck re-oriented the class by segregating the true worm like forms. He advanced to a considerable extent the classification of Echinoderms. The credit for classifying the animals into vertebrate and invertebrate goes to him.
Lamarck was the first man to give an idea of the causo-mechanical aspect of progressive evolution. He embodied these ideas in his book Philosophic zoologique (1809). The conceptions oudined in this book is better known as Lamarck’s ‘Theory of use and disuse’ or ‘Inheritance of acquired characters’.
Lamarck tried to establish his idea of progressive evolution in the following way:
1. Spontaneous generation of simple forms of life was followed by development of more complex organisms.
2. The environment governs the natural tendency of an organism to show structural changes.
3. Use or disuse causes variation in a structure.
4. Characters acquired in one’s lifetime is transmitted to one’s subsequent generations.
Arid literary style, personal eccentricity and pathetic struggle against poverty stood against the phenomenal rise of Lamarck. His over-proneness to speculation and poor attempts at Meteorology and at Chemistry discredited him to a great extent.
In his role as a systematist, he made important and lasting contributions.
Classical Microscopists # 12. Charles Darwin (1809-1882):
Darwin (Fig. 6.25) was the son of a doctor and the grandson of Erasmus Darwin who himself was a doctor and wrote on evolution. From his very boyhood he was interested in nature and never liked conventional schooling. His father wanted to make him a doctor and sent him to Edinburgh in 1825 to study medicine.
But he showed no taste for it. Gradually the influence of his father waned and his interest in medicine reached a vanishing point. He, in the next step, went to Cambridge to become a clergyman. He learned enough of Latin and Greek here. While he was wondering what to do next he got an offer to go as naturalist on the voyage of H.M.S. Beagle.
The Beagle 238 tons sailed in 1831 under Captain Fitzroy. The objective of the voyage was to survey South America to determine its longitude. Darwin was a naturalist without salary. Darwin worked in a narrow space with meagre equipment’s.
The voyage ended in 1835. The voyage was a voyage of discovery for Darwin. He collected enormous amount of data and spent rest of his days with the idea of Natural Selection stirring in his mind.
Some of Darwin’s scientific papers appeared in the Journal of Researches (1839-40). These papers dealt with his observations on the very peculiar animal and plant inhabitants of various isolated oceanic islands which had never been connected with continental lands.
These papers established him as a painstaking naturalist, remarkable for the general breadth of his outlook. He did commendable work on Barnacles and their allies, made investigations on mammalian fossil forms and wrote an admirable book on Coral reefs (1842).
In November 1859 Darwin’s monumental work on Evolution appeared in the book “Origin of Species by means of Natural Selection.” The book contains the conclusions arrived at by Darwin after twenty years of thinking and researches.
The origin of species created a revolution in biology and also in other departments of thought. It received a warm welcome soon after its publication and was accepted as a masterpiece by all thinking people.
The book certainly suggested a simple and apparently universally acting biological relationship to explain the process of change of form. The late nineteenth century became saturated with the concept of natural selection.
Scientists wanted to focus all their findings in the light of evolution and to quote Julian Huxley “Evolutionary studies became case books of adaptations.” Darwin’s idea of Natural Selection has stood the trial of time though it has undergone tremendous metamorphosis.
Classical Microscopists # 13. Schwann (1810-1882):
Theodor Schwann (Fig. 6.26) the German physiologist was born in Prussia in 1810. He was graduated in medicine from Berlin University in 1834. A few years after he joined the Berlin University as an assistant to Johannes Muller. Muller was a great teacher and greatest of all trainers of Anatomists and Physiologists.
His stimulus was a great cause in the uplifting of Schwann. Schwann was given the chair of Professor in the University of Louvin after the publication of-his cell theory. Later he was transferred to the University of Liege.
In his doctor’s dissertation he worked on the respiration of chick-embryos. He demonstrated the influence of organisms and lower fungi in fermentation and petrifaction. Thus it was an initial attempt to disprove spontaneous generation.
He also demonstrated
(1) Organic nature of yeast and
(2) The importance of pepsin in digestion.
He further discovered the striped muscles on the upper part of oesophagus and the envelope of nerve fibres called Schwann cell.
His greatest work was his classic book “Microscopic investigations on the accordance in the structure and growth of plants and animals (1839).” In 1838, he together with his botanist friend Schleiden (1804- 1881) advocated the cell-doctrine.
The essence of the doctrine is that:
1. Life starts as a single cell.
2. All living bodies are made up of cells.
3. Cells are always derived from preexisting cells.
The influence of cell-doctrine:
The cell- theory in its original form was imperfect and contained many fundamental misconceptions. However, the great truth that all parts of animals and plants are built of similar units was well substantiated. It was certainly the “master-stroke in generalization”. Moreover, it directed the attention of microscopists to the finer structures of the cell and paved the path of discovery of protoplasm, nucleus and chromosomes.
Classical Microscopists # 14. Mendel (1822-1884):
Gregor Johann Mendel (Fig. 6.27) was born in a peasant family in Silesia. He showed marked intelligence and ability in the village elementary school. He was sent to a good school at Leipnik. But poverty stood against him and he was forced to discontinue four years later.
At the age of sixteen he tried to continue his education at Olmutz Philosophical Institute supporting “himself by private tuition. With some initial difficulties he completed the two years course there.
He entered the monastery at Brunn in 1843 and was ordained a priest in 1847. He completed his theological studies and started working as a substitute teacher in Mathematics and Greek. The next year he took the examination for a teaching certificate and failed.
In 1851 he was sent to the University of Vienna, where he studied science. After that he came back to his convent where he passed the rest of his life first as a teacher of physics and natural science and later as the Abbot.
Mendel was fond of fruit-culture and gardening even from his boyhood. During his second term appointment as teacher, he performed a series of experiments with pea-plants in the garden of the monastery. His papers were published in 1866 and 1867 in the proceedings of the Natural History Society of Brunn.
His work contain experiments on the inheritance of individual (unit) characters in twenty-two varieties of garden peas. He selected certain constant and obvious characters of the pea plant such as length of stem, seed colour, seed form and made intensive cross-experiments to produce hybrids.
And thereafter he examined the results of self-pollination amongst the hybrids. Results revealed that in cross-breeding the parental qualities are not blended but that they retain their individuality in the offsprings. Each inherited trait is determined by a pair of differentiating factors (later named Gene by Johansen). These factors must separate, segregate and independently assort in each generation.
Mendel is regarded today as a great scientist, the ‘Father of Genetics’. He made epoch making investigations which added an entire realm to the world of Biology. His experiments have certainly laid the foundation for the science of Genetics.
The work of Mendel produced no immediate influence partly because of the fact that they were published in a journal with limited circulation and partly because of the fact that all attention was drawn at that time to the work of Darwin. His work remained unnoticed to the world and he never had the recognition due to him in his life-time.
In the year 1900 the great principles of heredity worked out by Mendel was re-discovered independently by three botanists, Correns, de-Vries and Tschermark. Their discovery was not a mere literary finding.
It was a need-based and deliberate search of the literature for confirmatory evidence for explaining the sequences of events already found. Thus the unrecognised papers of Mendel were taken out from the grave and made known to the scientific world.
From the beginning of the twentieth century the extension of Mendelian principles has begun. Now it ranks as one of the greatest discoveries in the study of Genetics.
Classical Microscopists # 15. Weismann (1834-1914):
August Weisihann (Fig. 6.28) was born in Frankfort in 1834. He became a graduate in medicine in 1856 from Gottingen. He started practicing medicine for some time. He never liked the profession and started working with microscope on embryology and morphology.
He was encouraged by Leuckart. He joined Freiburg in 1863 and became the Professor of Zoology there in 1867. Besides being a scientist he v as an accomplished musician.
Weismann developed with great theoretical skill his conception of the continuity of substance from parents to offsprings in his germ plasm theory and published it in his book “The Germplasm” (1893). Weismann thought that the offsprings resemble the parents because it is derived from the germ plasm of parents.
The body cells or somatoplasm act as vehicle for the conveyance of germ cells. The body cells nourish, protect and carry the germ cells to the offsprings and they do not convey any of their substances. The germ cells transmit an inconceivable complex inheritance.
The germ substances pass through coundess generations. In attempting to explain inheritance in detail he assumed the presence of distinct units embedded in the protoplasm of germinal elements. He called these units as Biophores.
The book “The evolution theory” (1904) is another important contribution of Weismann.
The book contains according to Thomson the translator:
(i) Illumination of the process of evolution with a wealth of fresh illustrations,
(ii) Germ plasm concept as valuable working hypothesis.
(iii) Abandonment of the concept of inheritance of acquired characters,
(iv) Further analysis of the origin of variation and
(v) Extension of selection principle of Darwin.
He -also wrote an autobiography “The Lamp” in 1903.
Weismann’s germ plasm theory is primarily a theory of heredity. His views have been a field of controversy. Following on Weismann, scientists became divided into two schools. One school accepted the theory of Lamarck while the other school rejected it.
The views of Weismann have passed through various stages of remodelling since it$ publication. It has become connected with other considerations to become the full-fledged theory of evolution known as Weismannism. He undoubtedly is the father of contemporary genetic theory.
Classical Microscopists # 16. De Vries (1848-1935):
DE VRIES (1848-1935) Hugo De Vries (Fig. 6.29) was born in 1848 at Haarlem, the Netherlands. He had his education at Leiden, Heidelberg and Wurgberg. He was appointed a lecturer at the University of Amsterdam and after few years held the chair of Professor of Plant Physiology. Following retirement in 1918 he kept himself engaged in research on mutation and evolution.
He made extensive experiments with plants like evening primrose (Oenothera Lamarkiana) and was amazed to find the sudden appearance of different species of this plant. These sudden variants bred true to give rise to new forms. He termed the variations as mutation.
His book, “The mutation theory” (Die Mutation theory) published in 1901 contains his notion that mutation is the universal source of origin of species. His mutation theory states that “species have not arisen through gradual selection accumulated for hundred or thousands of years but has appeared by sudden jumps and transformations.”
Though he laid due importance on Natural Selection as its being the sole agency for perpetuation and improvement of favourable variations, his theory became somewhat antagonistic to that of Natural Selection.
The reason behind this antagonism is that the conception of Natural Selection takes for granted that Natural Selection acts by accumulating slight, successive, favourable variation and not by great or sudden modifications.
In his other book “Intracellular Pangenesis” (1889) he developed a special theory of heredity related to that of Darwin. According to this theory hereditary characters in organisms may vary independent of one another or may combine with each other.
He introduced Pangenes which were hypothetical material entities representing these individuals. His concept of Pangene is that the Pangenes remain within the nucleus, multiply and come out of the nucleus to determine the form and activity of the tissue.
He independently rediscovered Mendelian principles of heredity, verified them and could realise their real implications.
De Vries opened up a new period of investigation of the phenomenon of heredity. Towards the end of nineteenth century biologists had no idea about the cause of genetic variation. His mutation theory provided a first-hand information to this burning question.
His work was based on experiments, and gave a great stimulus to experimental studies.
He made important contributions to the study of origin of species and also pointed to the fact that in analysing the process of organic evolution many diverse factors are to be taken into consideration.
The theory of De Vries also provided an incentive towards exploration. Davenport, Tower and many others proved conclusively that species may arise by slow and steady accumulation of minute variations. They never denied the role of mutation in species formation but showed at the same time many evidences of evolution without mutation.
Classical Microscopists # 17. Wolff (1738-94):
Caspar Friedrich Wolff was born in Germany in 1738. Little is known about his life and early educations. Even his portrait is not available. He could not get a foothold in any of the German universities because of negligence and hostility to his work. In 1764, he went to the Academy of Sciences at St. Petersburg being invited by the Catherine of Russia. He was there for thirty years.
Wolff, at the age of twenty-one published his book, Theory of Generation. The book consists of three parts—one devoted to the development of plants, one devoted to the development of animals and the third one to theoretical discussions.
He showed that organs of plants like root, leave, etc., are developed by a process of differentiation from uniform tissue At the tip of growing root or shoot and thus indicating that the region of growth of these structures consists of an area of undifferentiated tissue.
The development of organs of animals also follows the same rule as that of plants, i.e., development from apparently homoge neous tissue which at the beginning is not stamped with its ultimate fate.
Wolff’s best work is on the development of intestine of chick (De Formatione Intestinorum) published in 1768. The book shows his originality and strong power of observations and inferences. According to Von Baer “It is the greatest masterpiece of scientific observation which we possess”.
Wolff’s name is still associated to a structure peculiar to the embryo. It is known as ‘Wolffian body’ or ‘primitive kidney’. He could trace the development of this structure from undifferentiated tissue mass. The structure does not exist in adult stages of vertebrates excepting certain fish.
Wolff was the pioneer to advocate the process of Epigenesis in development. Epigenesis, as it stands, is an event in which something appears by development which was not before even in the rudimentary condition.
Epigenesis concept was opposed to the then existing view of Preformation. The views of Wolff in his life time could gain no currency and as a result the progress of Embryology was retarded for another fifty years or so.
Wolff could very well establish the fact that development is a gradual process. But the explanation of his theory of development was unsatisfactory. He had no idea of germinal continuity, neither the idea had emerged in his time.
He assumed a total lack of organisation at the beginning and ascribed development as a miraculous phenomenon through the action on the egg of a hyperphysical agent. Wolff thus made the same quandary as his predecessor when he tried to explain development.
Wolff was a man of great power and had much originality. His influence was retarded for a long time because of an uncongenial atmosphere. He should be recognized as a pioneer investigator who influenced future embryologists like VonBaer.
Classical Microscopists # 18. Von Baer (1792-1876):
Karl Ernst Von Baer (Fig. 6.30) was born at Piep in Astonia. He intended to become a physician. He was, however, diverted from this aim by an interest in Anatomy and Comparative Embryology. After wandering through several universities, he stayed for some time in Wargburg.
He then joined Konigsberg University in 1817 as Professor. In 1834 he accepted a chair at St. Petersberg and passed there the rest of his life. In the later part of his life he developed some interest in Anthropology.
Von Baer’s name is associated with the following advances in ‘Embryology.
1. The discovery of mammalian ovum.
2. The proposition known as germ layer theory.
3. Von Baer’s law concerning similarities in individual development and development of the race.
4. The discovery of notochord.
Of these the first appeared in his book “On the origin of the mammalian and human egg” (1827).
The other information were given in his book “Developmental History of Animals”.
In the matter of germ layers he showed that during development in certain animals, the ovum divides to form layers of tissue. These layers give rise to various organs of the body. Further, in certain groups of animals specific organs develop from specific layers.
He distinguished four such germ layers—an outer and an inner which develop first and the two intermediate layers that are later on budded off from these layers.
Van Baer’s law consists of the following generalizations:
1. In development general characters appear ahead of special characters.
2. From the more general characters are developed the less general characters and finally the special ones.
3. During the course of its development the member of one species diverges continually from that of another species.
4. During development higher animals pass through stages resembling the stages of development of lower animals.
Von Baer discovered and described for the first time the development of notochord or chorda dorsafis.
Von Baer was instrumental in enriching Embryology in three counts.
First of all he set a higher standard for all work in embryology. Secondly, he advocated the germ layer theory. In the third plan, he brought the spirit of comparative embryology.
Von Baer’s embryological doctrine is of tremendous historic and practical importance. At a later age when organic evolution received general acceptance, structural relationship came to be explained in the light of relationship with descent and as a corollary the process of development came to be the acid test of structural relationship.
Von Baer has been made dignified with the tide of “Father of modern embryology”
Classical Microscopists # 19. Haeckel (1834-1919):
Ernst Haeckel (Fig. 6.31) was born in Jena in 1834. He studied with Johannes Muller, Virchow and Gegenbaur. Haeckel had a prodigious literary output. He held the Professorship in Zoology at Jena till 1909. He kept himself busy with the great liberal intellectual movement of his time and during the last part of his life he devoted himself to romantic natural philosophy.
His first important contribution is on the Radiolaria of the Mediterranean (1860). He himself was a good artist and the illustrations of the memoir were done by him. It still serves the purpose of a standard reference book in this line.
He is best known for his “The Fundamental Biogenetic Law” or “The Theory of Recapitulation”, which was embodied in his book “Generelle Morphologie”, (1866). The theory may be briefly stated as “Ontogeny is an epitome of Phylogeny”.
Haeckel coined the term ‘Ecology’. In 1872 he published a monograph on calcareous sponges. He tried to classify them on the basis of their canal system. The system is still followed by many. He also published another monograph on the group Monera. He tried to establish that this group lack nucleus. Nucleus, however, was found to be present in them by later workers.
Haeckel was the warmest exponent of Darwinism in Continental Europe.
It is almost impossible to estimate Haeckel’s place in the history of biology. There is no denial that he had amazing influence on the biological thought in the late nineteenth and early twentieth centuries.
Few of his work have survived the test of science and many of them have been subjected to heavy criticism.
His work are of historical importance and now rest peacefully on the remote shelves of the Library. Yet they are rich with contributions which are still fundamental to the fabric of scientific thought.
Classical Microscopists # 20. Balfour (1851-1882):
Francis M. Balfour (Fig. 6.32) was born in 1851. During his preparatory days in the university he was a good student. Being encouraged by his teachers he stepped into embryology. He entered into the subject with great intensity and by dint of his talent, devotion and hard labour soon became recognised.
He became a Professor at Cambridge. He died untimely at the age of 31. He was a great stimulator of research and at the time of his death there were as many as twenty students working under him.
His book “Comparative Embryology” (1880-81) in two volumes is a book of ‘priceless value’. The volumes contain enormous information about the work of past embryologists.
At the period of Balfour, observations on the development of many animals accumulated in great number. But the information remained scattered in monograph, periodicals and transactions of learned societies. Balfour went through all these, assimilated them and took up the Herculean job to put them into an organised whole. He was successful in doing so and thereby hinted at the present tendencies in embryology.
Classical Microscopists # 21. Hertwig Oscar (1849-1922) and Hertwig Richard (1850- 1872):
These two brothers studied at Jena under Haeckel and secured degrees in medicine from Bonn. Oscar (Fig. 6.33) became the Professor of Anatomy first at Jena and then in Berlin. Richard held the chair of Professor of Zoology first at Konigsberg and then at Bonn. They cooperated closely on many investigations on anatomy and embryology.
The two together published many monographs. They studied the comparative anatomy of the coelom extensively and put forward the theory of coelom which contributed much to the understanding of comparative anatomy at the early stage of individual development.
Oscar studied fertilization and was the first to describe the phenomenon of fusion between sperm and ovum during fertilization. Richard studied cytology and nucleus of protozoa and investigated the role of protozoan nucleus in vegetative reproduction.
Classical Microscopists # 22. Roux (1850-1924):
Wilhelm Roux was a student of Haeckel and studied medicine at Jena. For his doctorate degree he submitted a thesis on the haemodynamic factors that control the formation of blood .vessels. The work of German Zoologist, August Weismann influenced him much and he devoted himself to the cause of experimental embryology.
In a series of writings collected as “The developmental struggle of the parts within the organism” (1881) he presented his view of a mechanical basis for functional adaptation of the body parts to each other. Any investigation of function needs experimentations. So in order to seek a basis for his developmental mechanics (Entwicklungs mechanik) he switched over to experiments on embryo.
Making casual analysis as his aim he performed a simple type of experiment on frog’s egg. When the frog’s egg was at the two-celled stage of cleavage he injured one of the two first formed blastomeres. The remaining one after the experiment developed into a ‘half-embryo’.
Roux interpretated his results in the following way: There are two types of differentiation—self-differentiation (independent or mosaic development) and correlative dependent differentiation (interaction of cells or groups of cells).
In his experiment, the development of one cell into a half embryo is suggestive of the fact that each cell develops independently of its neighbour and conversely total development represents a summation of partial mosaic developments.
His paper “contribution to the developmental mechanics of the embryo, on the artificial production of half- embryos by destruction of one of the first two blastomeres and post generation of the missing half of the embryo” was published in 1888.
He established the journal “Archiv fur Entwicklungs mechanik der Organismen.” The first volume of the journal was published in 1894-95. It is the first international journal for analytical embryology. The journal is in operation till date and now it has been named after him as “Roux Archiv.”
The conclusions of Roux were later proved to be incorrect. But the experimental approach of Roux was significant on many counts. In the first place it brought about a new trend in method and attack on .the process of embryonic development.
In the second place his experiments shifted the emphasis from descriptive to experimental embryology. In the third place it brought the old problem of epigenesis in the lime light. The experimental embryology of today rests on the foundations laid by Roux.
Classical Microscopists # 23. Spemann (1860-1941):
Hans Spemann was born in 1860 in Germany. He carried out extensive researches on developing newt’s egg for over a period of more than twenty-five years and raised the standard of experimental embryology to a higher level.
His constriction experiments:
During the year 1901-1903 he performed a series of experiments in which the blastomeres of the two-celled stage of newt’s egg were separated by tightening a human hair along the first cleavage furrow. In some experiments each blastomere produced one miniature but whole embryo.
In the majority of the cases, however, one of the blastomeres produced a small but whole embryo and the other one produced a ball of unorganised living cells. These differences in the results were due to the variable position of the first cleavage plane with reference to the median plane of the future embryo.
Thus when the first cleavage plane appears in line with the median plane two dwarf embryos result. On the other hand, when the first cleavage furrow appears at right angles to the median plane, one blastomere gives a whole embryo and the other produces an abortive-cell mass. If constriction is made in early gastrula, a similar result of the second type is obtained.
From these experiments Spemann concluded that as early as the two-celled stage there appears a qualitative change between the dorsal half and ventral half. The dorsal half is equipped with the quality to form an embryo whereas such a quality is absent in the ventral half.
In the year 1918 he made transplantation experiments with Triton embryos. When he transplanted a small piece of ectoderm of one early gastrula to another gastrula of the same age, the transplanted piece developed in accordance with its new position. But if the dorsal lip of the blastopore is grafted in the same manner, it would behave in a different way.
The grafted dorsal lip will organise an embryolike body with neural tube, somite and notochord in the new site. From these experiments Spemann inferred that the dorsal lip was already determined and represented a ‘centre of differentiation’.
Spemann further wanted to know how much of self-differentiation ability is present in the grafted material (dorsal lip of blastopore) and how it was due to induction. The answer to this question was made available by grafting a dorsal lip of one species of Newt to another species having more darker pigments and which is supposed to behave as marker.
Such experiments revealed that both the dorsal lip and the host embryo participated in the formation of the second embryo. The graft contributes the chorda-mesoderm and the host contributes the nervous system. He called the dorsal lip of the blastopore as the organizer.
The discovery of the organizer and the knowledge about its action opened up new avenues in experimental embryology. It demonstrated clearly that the steps in development are interrelated and one step is a necessary condition for the step above it. Thus the epigenetic concept of early embryologist proved true. Spemann won Nobel prize in physiology and medicine in 1935.
Classical Microscopists # 24. Morgan (1866-1945):
Thomas Hunt Morgan was born in 1866 at Kentucky. After completing his undergraduate studies at the Kentucky College of Agriculture and Mechanical Arts, he entered John Hopkin’s University in 1886 and studied Embryology. He obtained his Ph.D. degree in 1890. He then joined Brym Mowr as Associate Professor of Biology in 1891 and stayed there up to 1904.
During his stay here he did his embryological work. He was made Professor of Experimental Biology at Columbia University. He held the chair here up to 1928 and then joined California Institute of Technology. He organised the Division of Biology and remained there till his death in 1945. He used to make summer trips to Woods Hole to utilise his vacation on the studies of marine animals.
Morgan has more than two hundred scientific papers and eight books to his credit. Morgan was interested in Embryology and the process of differentiation at the beginning of his research career. Later he turned to Genetics. Rats and mice were his first laboratory animals but recognising the advantages of the fruit fly Drosophila, he made the fly his experimental material and developed studies on heredity and variation.
The results of the research of Morgan and his associates like Sturtevant, Bridges and Muller led to a spries of publications on genetical work. The classical book of this team. “The mechanisms of Mendelian heredity” (1915) is a wonderful attempt to explain Mendelian principle of heredity on chromosomal basis.
The next edition of the book was published in 1923. It contained many revisions indicating the rapid pace at which accumulation of knowledge is taking place. The book “Sex linked inheritance in Drosophila” (1916) is stamped with the understanding and significance of linkage. “The theory of the gene” (1917) is another significant contribution of Morgan which has laid the foundation of basic research in genetics.
He also made contributions on regeneration and development of marine animals.
The work of Morgan and his associates are the most important ones in genetics after Mendel. Introduction of Drosophila, the Cinderella of genetics as a laboratory material gave a tremendous pace to genetical researches. Morgan formulated many principles which accelerated the investigations in hereditary mechanism.
Morgan was recipient of Darwin Medal (1924), Nobel Prize in Medicine (1933) and Copley Medal of Royal Society (1939).
Classical Microscopists # 25. Muller (1890-1967):
H. J. Muller was born in New York in 1890. He did his undergraduate and graduate work at Columbia University. In 1912 he joined Columbia University as a member of the faculty of Biology. In 1920, he became an Associate Professor of Zoology of the University of Texas. Later he held the chair of Professor of Zoology at the Indiana University and kept himself busy with his research on heredity.
During his days at Columbia he was associated with Morgan and was an active member of the “Fly-squad” of Morgan. Along with Morgan he did notable work on the linear arrangement of genes on the chromosomes and on the mechanism of heredity.
Muller was interested to know the underlying causes of gene change or mutation. He applied various means like heat, drug, poison, etc. on Drosophila with an idea to induce mutation. But mutations were exceedingly rare. In nature mutation occurs once in a million.
So he wanted to find out a scientific device so that frequent mutations may be produced. Such induced mutations will provide an opportunity to make a probe into gene and chromosome.
But the genes lie in well protected condition. To reach the genes is a problem. Muller was struck by the idea that gene is a molecule and its properties depend upon its chemical composition and if that be so they can be shot or altered by electron bombardment from X-rays or rays of shorter length.
Muller and his associates put hundreds of Fruit flies in gelatin capsules and subjected them to X-rays. The X-rayed flies were then mated with untreated mates and there were mutations, mutations and mutations.
The full significance of the discoveries of Muller became realised. For the first time man could know how new comes into the world and how the change or the new character is nursed by natural selection to fill most of the niches of the earth. Muller was awarded Nobel prize for his “Discovery of the production of mutations by means of X-ray radiation” in 1946.
Classical Microscopists # 26. Watson (1928):
J. D. Watson was born in Chicago in 1928. He did his B.S. from Chicago University in 1947. After obtaining his Ph.D. degree in 1950 from Indiana University he accepted a Post-doctoral fellowship and came to Copenhagen in 1950. He joined the Cavendish Laboratories of Cambridge University in 1951 and stayed there up to 1953.
Here in collaboration with Francis Crick he elucidated the double helical structure of the wonder molecule of DNA in 1953. Its discovery marked a new approach to scientist’s attempt to solve the complexities of life. Now he is working as the Professor of Biology, Faculty of Harvard University. He is working out problems of protein synthesis and replication of virus.
He along with Crick and Wilkins was awarded Nobel Piize in Medicine and Physiology in 1962.
Classical Microscopists # 27. Pauling (1901-):
Linus Pauling was born at Portland, Oregon. He graduated from Oregon State Agricultural College. He went to Munich to study under Arnold Sommerfeld and then to Copenhagen and Zurich. He had the honour of working with Neils Bohr and Erwin Schordinger.
Under their stimulating influence he became interested on the forces that bind atoms into molecules. His famous book “The nature of the chemical bond” is an outcome of his initial interests in Physical Chemistry. Later he worked on protein structure and could discover with his associates that the protein is another helical coil. He was awarded Nobel prize in 1954.
Classical Microscopists # 28. Khorana (1922- ):
Hara Gobinda Khorana (Fig. 6.34) was born in Raipur, India in 1922. He became a graduate in 1943 from the Punjab University. He did his M.Sc. from the same university in 1945. For his Ph.D. degree he joined the Liverpool University and after obtaining the degree in 1948 he came back to India.
He stayed in India for about eight years (1952-60) as Head of Organic Chemistry group of the B.C. Research Council. He was invited to Rockefeller Institute, New York as a visiting Professor in 1958. Later he settled in America. He worked in high positions in a number of American Universities.
Khorana’s work in Khorana’s language is “A Chemist’s adventure in Biochemistry”. In such an adventure he has already completed his work of chemical synthesis of naturally occurring co-enzyme-A.
His book “Some recent developments of chemistry of phosphate esters of biological interest” is a new approach in this line. He has numerous research publications to his credit. His work on ‘Genetic Code’ is an epoch making discovery about the wonder molecule-DNA. On the basis of this work he has been awarded Nobel Prize in 1969. At present he is working on artificial synthesis of genes.