The essay traces the history of the development of histology up to the end of the nineteenth century with special reference to some of the persons who helped to establish it as a separate discipline within the biological and medical sciences and the techniques that underpin it, notably the introduction of staining techniques and the development of the apochromatic microscope.
There is nothing more difficult than to establish the earliest date at which some very common procedure was first used. Such dates, apparently fixed, have a way of becoming unfixed as the history of the subject is further studied .
Histology, the study of the finer structures of animals and plants with a microscope, started to emerge as a distinct discipline within the biological and medical sciences during the early part of the nineteenth century, although the study of tissues with the naked eye and magnifying glasses can be traced back to Marcello Malpighi (1628 - 1694) who can rightly be regarded as the person who founded microscopic anatomy. In his book Epistolae de pulmonibus of 1661, which he dedicated to his mentor Giovanni Alfonso Borelli (1608 – 1679) , Malphigi described the small air sacks (alveoli) of lungs and the network of minute blood vessels which join the arteries to the veins (anastomoses, capillaries). (Borelli founded the ‘Iatromechanic School’ who chose to explain the workings of the animal body purely on mechanical grounds, and attributed all physiological and pathological phenomena to the laws of physics).
The essay consists of three interrelated sections:
- A short glossary of some of the terms used;
- Biographical notes on three nineteenth century scientists who through their own work and that of their students were instrumental in introducing microscopy to biological and medical research; and
- An account of improvements in the technical underpinnings of histology that occurred during this period -- notably the introduction of staining and the development of the apochromatic microscope -- that contributed to the explosion of knowledge of the finer structure of humans, animals and plants that occurred during the later half of the nineteenth century.
‘Biology’, derived from the Greek ‘bίos’, meaning life, and the suffix-logy, meaning knowledge, may date from Karl Friedrich Burdach’s (1776 - 1847) book Propädeutik zum Studium der gesammten Heilkunst which was published by Breitkopf and Härtel of Leipzig in 1800.
The term ‘histology’, from the Greek ‘hίstos’ for a ‘web’, appears in the title of Carl Mayer’s (1787 – 1865) 41-page book Ueber Histologie und eine neue Eintheilung der Gewebe des menschlichen Körpers which was published by Adolph Marcus of Bonn in 1819. But the book contains no histological information and ‘histology’ does not appear in the text. The book is the printed version of an address he gave before his first lecture as Professor of Anatomy, Physiology and Pathology at the newly established Royal Prussian Rhein University at Bonn. In the lecture he divided the body into twenty-one ‘Systems’ and gave a brief description of each system.
The word ‘tissue’ comes from the Old French ‘tissu’ for a belt of woven material. Its use in scientific writing is attributed to Marie-François-Xavier Bichat (1771 – 1802) who published Anatomie générale, appliqué à la physiologie et à la medicine in 1801.
History has many contributors and histology is no exception. However it is possible to single out three persons whose contributions were of inestimable value:
- Johannes Petrus Müller (1801 – 1858),
- Rudolf Albert Koelliker (1817 – 1905), and the oldest of the three,
- Jan Evangelista Purkynĕ (1787 – 1869).
The fact that all three were German speaking reflects Germany’s domination of biological and medical research during the nineteenth century.
Johannes Müller was born at Koblenz on 14 July 1801; his father was a cobbler. As a schoolboy he liked classics and translated a text of Aristotle. Although destined for the priesthood he decided at the age of 18 to go to the newly established University of Bonn to study medicine and graduated in 1822. The next year he continued his studies at Berlin where Karl Asmus Rudolphi (1771 – 1832) was professor of anatomy and physiology. Eighteen months later he returned to Bonn to teach physiology and comparative anatomy and became a full professor in 1830. When Rudolphi died in 1832, the chair was offered to two eminent professors who both declined the invitation. On hearing this Müller wrote to Baron Karl von Altenstein (1770 – 1840), the minister responsible for the appointment, putting forward his eminent suitability for the post. He started in Berlin in early 1833 and taught anatomy, physiology and later pathology, encouraging his students to use a microscope. A prolific experimenter, he argued against natural philosophy which was still being taught to medical students. He had a special interest in the physiology of speech, vision and hearing, and investigated the physical and chemical properties of body fluids: he noted a similarity between plant and animal cells. Author of many books his Handbuch der Physiologie des Menschen für Vorlesungen, which was completed in 1837, was widely used (an English translation followed soon afterwards). It is said he wrote on an average one scientific publication every seven weeks. Müller suffered from depression and periodically needed prolonged periods off work to recuperate; he may have taken his own life. It was only after his death that the university created separate chairs of anatomy, physiology and pathology.
Müller is recognized as one of the outstanding biologists of all time for his own contributions to medicine and biology (he also undertook many trips to the Baltic to study and classify fishes and marine invertebrates; he described several species of snakes). His impact is even greater if one considers the seminal achievements of some of his students:
Jacob Henle (1809 – 1885), who accompanied Müller to Berlin from Bonn, discovered the tubules of the kidney and ‘..... is often described as one of the great anatomists of all time and as the man who rendered to microscopic anatomy, the same service that Vesalius performed for gross anatomy’  ;
Theodor Schwann (1810 – 1882). In 1839 he, based on his own observations and those of others including his friend Matthhias Schlieden (1804 - 1881), formulated the Cell Doctrine which stated that plants and animals are made up of myriads of individual cells;
Robert Remak (1815 – 1865), a brilliant Pole, who preferred to remain Müller’s assistant rather than applying for professorships elsewhere. Amongst his many contributions to biological science was the one of 1841 when he reported that, contrary to the prevailing opinion that new cells arose spontaneously from the surrounding fluid, he had observed that the red cells of chicken embryos were the result of a division of pre-existing cells;
Rudolf Virchow (1821 – 1902) who established pathology as a separate discipline within the medical sciences. He qualified in Berlin in 1839 where he continued his studies in pathology. In 1848 he had to leave Berlin because he took an active part in the political revolutions that swept through Europe that year. On hearing this the University of Würzburg immediately recruited him as Professor of Pathology, and he stayed there until 1856 when he returned to Berlin as the first Director of the Pathological Institute. While at Würzburg Virchow laid the groundwork for his celebrated book ‘Die Zellularpathologie in ihrer Begründung auf physiologische und pathologische Gewebelehre’, a series of twenty lectures which was published in 1863. In the second lecture, which had been given on 17 February 1858, he stated: ‘Where a cell arises, a cell must previously have existed (Omnis cellula e cellula), just as an animal can spring only from an animal, a plant only from a plant’  ; and
Albert Koelliker, who became the doyen of human histologists of the second half of the nineteenth century was born on 6 July 1817 in Zurich where his father was a bank official. He went to Zurich University in the spring of 1836 and studied chemistry, geology, physics, zoology and natural philosophy before turning to medical subjects. In 1839 he spent a semester at Bonn before going to Berlin where his teachers were Johannes Müller and Jacob Henle. Returning home after three semesters he took with him a large microscope made by Wilhelm Schiek (1790 – 1870). When Henle came to Zurich in 1840 as Professor of Anatomy Koelliker became his assistant. Henle’s stay was short-lived and when he left for Heidelberg in May 1844, the 27 year old Koelliker became Professor Extraordinary of Physiology and Comparative Anatomy. With a growing reputation as a teacher and researcher it was not long before he was recruited to join the medical faculty of the University of Würzburg which was fast becoming one of the foremost institutions of its kind in Germany. He started in September 1847 and remained there the rest of his life. Koelliker completed the the first volume of Handbuch der Gewebelehre des menschen für Aertze und Studirende in 1852; the second volume was published in 1854.
This was not the first textbook on human histology. Apart from Mayer’s little book, there was Henle’s Allgemeine Anatomie published in 1841, Alfred Donné’s (1801 – 1878) Cours de microscopie complémentaire des etudes médicales of 1844, and Arthur Hill Hassall’s (1817 – 1894) The microscopic anatomy of the human body, in health and disease of 1849. Koelliker’s book, consisting of 637 pages and 313 woodcuts, was just so much better than its predecessors in its content, lay-out and clarity of expression. The book was translated into English (London and Philadelphia) in 1854, and into French and Italian in 1856. The second volume of the sixth and final edition was published, as were all the previous editions, by Wilhelm Engelmann (1808 – 1878) of Leipzig in 1896. A third volume to complete the sixth edition was edited by Viktor von Ebner (1842 – 1925), Professor of Histology in Vienna, and published in 1902.
In 1848 Koelliker and fellow Würzburger Carl Siebold (1804 – 1885), a noted zoologist, co-founded Zeitschrift für wissenschafliche Zoologie. The journal was soon regarded as one of the leading biological journals and it was through its pages that the scientific world heard of new biological discoveries . One of the scientists who benefitted greatly from this reporting was the Spaniard Santiago Ramón y Cajal (1852 – 1934) who was interested in the micro-anatomy of the nervous systems of animals and humans. Feeling that he was isolated in Spain because of geography and language, and that he had not received due recognition for work he had published, Cajal decided to join the German Anatomical Society. In October 1889 he went to their meeting in Berlin where he met Koelliker. In his autobiography Cajal tells what happened next:
I am deeply grateful to the distinguished master of Würzburg (through whose) great authority ..... my ideas were rapidly disseminated and appreciated by the scientific world ...... (He) carried his goodwill so far as to learn Spanish in order to read my earliest communications ..... personally translating for his (journal) the text of a work of mine on the hippocampus, etc. 
Koelliker seems to have been a fair judge of other scientists’ work and from 1901 onwards repeatedly nominated Cajal and the Italian Camillo Golgi (1843 – 1926), whose silver stain of 1873 was to revolutionize the study of the nerve cell (neuron) and form the backbone for Cajal’s studies, for the Nobel Prize for Physiology or Medicine. They shared the prize of 1906 but sadly Koelliker could not attend the Nobel Prize awards ceremony in Stockholm on 10 December that year because he had died at the age of 88 on 2 November the previous year.
Jan Purkynĕ, ‘..... one of those men who may be called milestones on the road to knowledge’ , was born on 17 December 1787 in Libochovice in Bohemia where his father was an estate manager. After gymnasium he became a novitiate in the Piarist Order, but left in 1807 to study philosophy in Prague before switching to medicine in 1822. In Praque he met Johann Wolfgang Goethe (1749 – 1832) with whom he had a life-long friendship -- Johannes Müller was also a friend of Goethe and like them interested in the phenomenon of vision.
Purkynĕ graduated MD in 1819 and four years later accepted, against much opposition, the chair of physiology and pathology at the University of Breslau (now Wroclaw in Poland). He worked in Breslau for 27 years before returning to Prague during the Easter of 1850 as professor of anatomy and physiology; he was then 63 years old. Having acquired a large achromatic compound microscope made by Simon Plössl (1794 – 1868) of Vienna in 1832, he and his students began a systematic study of the micro-anatomy of animal tissues. In 1836 his most eminent student, Gabriel Valentin (1810 – 1883) with whom in 1833 he was the first to observe ciliary movements, described the detailed structure of a nerve cell. The next year Purkynĕ followed this up with a description of the large neurons with many branching dendrites that are found in the cerebellar cortex - the Purkinje cells (fibres that conduct the electrical impulses within the heart also carry his name). Purkynĕ and his assistants worked tirelessly and in time a cerain rivalry developed between them and Müller and his group in Berlin.
Whereas Müller’s protégés, for example Schwann, Henle and Virchow, produced books and monographs that attracted a great deal of attention and were accompanied by a fanfare from the reviewing journals, prior discoveries of Purkynĕ’s group were recorded mainly in doctoral theses or in lectures and brief reports. It was not until the twentieth century that serious efforts were made to restore his position as a major contributor to the science of microscopic anatomy, and one of the pioneers, if not the principal pioneer, of the cell theory. 
Despite the excellence of Purkyně’s work, the university officials were unwilling to meet his demands for space and equipment so that much of his research and teaching was carried out in his own home laboratory. It took the university nine years to agree to buy him the Plössl microscope. Politics and language may also have played a rôle because Purkynĕ promoted the Czech language and culture. Chapter 9 of The Birth of the Cell (1999) is headed The Cradle of Histology, but in History of Physiology (1973)  the accolade is shared between Müller’s laboratory and Purkynĕ’s Institute; the latter was opened on 8 November 1839 in a small brick building that was once a shed attached to the anatomy department.
Good histology needs well-made ‘slides’ and a good microscope.
The making of acceptable histological slides, a multi-step process consisting of fixation, mounting, cutting and staining, took a long time to perfect, and so did the development of the apochromatic microscope. But by the end of the nineteenth century both had been accomplished
Duke Frederico Cesi (1585 – 1630), who founded the Accademia dei Lincei in 1603 , teased out the tissues of the bees he was so fond of before taking a closer look at their structure with his microscope. His fellow Lycean Academy member Giovanni Battista Hodierna (1597 – 1660), however, allowed the insects he was interested in to decompose before examining them with a microscope; he could separate the eye of a fly into four separate layers.
This practice of teasing out or squashing flat the tissues to be examined meant that the relationship of the various cells to one another was disturbed and that only low magnifications were possible before the images became too blurred. In 1666 Robert Boyle (1627 – 1691) reported that immersing tissues in ‘spirits of wine’ prevented post-mortem decay and thus helped to preserve the natural state of the tissues. This immersion had an additional benefit: the tissues had hardened sufficiently for thin sections to be cut with a sharp knife.
In October 1833 the editor of the Edinburgh New Philosophical Journal recounted a conversation he had with a Professor Jacobson of Copenhagen (probably Ludwig Jacobson, 1783 – 1843) about chrome which had been detected in red lead ore from Siberia in 1797 by Louis-Nicolas Vauquelin (1762 – 1829). The professor told him that ‘..... chromate of potash (was) highly important as a means of resisting fermentation and putrefaction .....’ . In 1840 Adolph Hannover (1814 – 1894) wrote Jacobson a letter saying that this treatment made it possible for him to cut thin sections of the eye and brain.
Osmic acid was introduced as a fixative in the 1850s by Franze Schulze (1815 – 1921) of Rostock and his pupil Max Schultze (1825 – 1874), but its use was slow to become accepted because the acid was expensive and labile; moreover, penetration was slow and only a small piece of tissue could be fixed at any one time.
Formaldehyde (formalin), known to everybody, is a naturally occurring organic compound which is equally good for the preservation and for the fixation of tissues. The solution was in common use by the end of the nineteenth century having been discovered by ‘accident’ in 1865 by the Russian chemist Alexander Butlerov (1828 – 1886).
The idea of freezing the tissue was bandied around during the 1820s, but it was the experience of Benedikt Stilling (1810 – 1879) that prompted the exploitation of this technique for overcoming the fact that, with the exception of bone or cartilage, animal tissues were too soft for fine sectioning. Arriving at work on 24 January 1842, Stilling found that he had by accident left a piece of spinal cord on the windowsill of his laboratory the night before. On retrieving the tissue, he found it was hard enough for him to cut a transverse section through it and, when he looked at the cut surface with a magnifying glass, he saw nerve bundles . Later, when freeze-drying became better known, there appeared on the market many devices (microtomes) of various sizes and complexities that used either ice and salt, or the cooling effect of evaporating ether or carbon dioxide, as freezing agents.
While attempts to harden the tissue were under way, other scientists were looking for a substance in which the hardened tissue could be embedded before being cut into thin slices. Rudolf Heidenhain (1834 – 1897) introduced gum Arabic while Salomon Stricker (1834 – 1898) advocated a mixture of wax and oil. Andrew Pritchard (1804 – 1884) in 1832 used a drop of a gum/isinglass mixture (isinglass is an almost transparent gelatine obtained from the bladders of fish) on a glass slide which he covered with a mica disc. The same year Canada balsam, a turpentine made from the resin of Abies balsamea appeared on the scene, and in 1869 Edwin Klebs (1834 – 1913) reported that he had for some years embedded his specimens in paraffin.
In England mounting of tissues became a profession whereas the German researchers prepared their own mounts.
As the magnification and focussing qualities of microscopes improved, it became increasingly obvious that consistently thinly cut tissue slices were needed, something that was difficult to achieve with hand-held razor blades. Valentin, Purkynĕ’s assistant, made a knife with two closely screwed together blades that was drawn rapidly through the tissue. This device led to the invention of the microtome, the word being derived from the Greek micrόs (small), and témneîn (to cut).
Although there were claims that an English optician invented such a device in 1770, it was the microtome made by Purkynĕ in the early 1830s that other scientists copied and improved upon. In 1857 Wilhelm His Sr. (1831 – 1904) reported that his instrument ‘.... has enabled (me) a precision in work by which I can achieve sections that by hand I cannot possibly create ‘  ; it was a matter of pride to him that by 1870 he had made more than 5000 sections with the instrument.
Stilling also introduced the concept of serial sectioning. In the later 1840s he published illustrated volumes which depicted 15x magnifications of transverse, longitudinal and oblique sections of the spinal cord, medulla oblongata, pons and cerebellum of animals and humans which had been cut with a razor dipped in alcohol.
The introduction of colouring agents -- dyes or stains – to improve the quality of microscopical observations, helped immeasurably to consolidate histology’s place in the family of medical sciences; the dyes were either extracted from natural products or concocted by chemists. Although most of this happened during the third quarter of the 1800s, an important early contributor was Felice Fontana (1730 – 1805) who in 1781 was the first to observe the nucleus and nucleolus of an animal cell; his work was the platform on which later microscopists built.
Carmine, a bright-red pigment derived from cochineal insects of Mexico, led the way and was introduced in 1770 by John Hill (1717 - 1775) who was interested in the histology of timber . Many years later, in 1851, Alfonso Corti (1822 – 1876), working in Koelliker’s laboratory in Würzburg, used a solution of alcohol and carmine to study the epithelial lining of the cochlea. But it was Joseph Gerlach (1820 – 1896), the influential professor of anatomy of Erlangen University, who was mainly responsible for the widespread use of carmine as a stain of microscopic slides. Although Gerlach was less successful when he stained nervous tissue with carmine, he was nonetheless confident enough in 1872 to put forward the idea that the cells of the nervous system, in contradistinction to those of the rest of the body, were all joined together to form a mesh - a concept that became known as the Reticular Theory .
The other important naturally occurring stain introduced during this time is also associated with Koelliker’s laboratory -- haematoxylin, an extract from the logwood Haematoxylon campechnianum. The extract as such is not a dye but becomes one, and changes its colour from red to blue when combined with alum, a process that Friedrich Böhmer (1829 - ?) perfected in 1865 .
Around 1853 an eighteen year old London chemistry student, William Henry Perkin (1838 - 1907), accidentally came across a purple dye while attempting to synthesize quinine. This dye, which he named mauveine, was the first member of the aniline family of dyes which were to revolutionize the commercial dyeing industry and contribute significantly to the advance of histology . Although Friedrich Beneke (1824 – 1882) in 1862 was the first to suggest the use of aniline dyes in histology, it was mainly due to Paul Ehrlich (1854 – 1915), who had an interest in both chemistry and histology, that this happened . In the 1870s Ehrlich undertook a systematic study of the aniline dyes and while doing so identified the different types of white cells in a blood film he had stained with methyline blue. He discovered that the addition of aniline oil to the solution enabled the dye to penetrate the membrane of the tubercle bacillus, which led to the development of the Ziehl-Neelsen (Franz Ziehl, 1859 - 1926, and Friedrich Neelsen, 1854 – 1898) acid-fast stain for tuberculosis. On 24 March 1882 Robert Koch (1843 – 1910) announced at a meeting of the Berlin Physiological Society that he had identified the tubercle bacillus as the cause of the disease.
The use of aniline dyes is also associated with Walther Flemming (1843 – 1915), professor of anatomy in Kiel, who was the founder of cytogenetics, the analysis of human chromosomes for the detection of inherited diseases. He had a particular interest in the division of animal cells, and during the 1870s had refined the techniques of fixation and staining with aniline dyes to such a degree that he could study the minutest details of the cell and its nucleus. It was Flemming who coined the words mitosis and chromatin, from the Greek for a ‘thread’ and ‘colour’ (red) respectively .
Another important development in staining was the introduction during the 1870s of double or counter staining by several scientists, notably Nicolaj Federovič Vysockij (1843 – 1922), lecturer and later Professor of Anatomy at the Imperial University of Kazan, Russia. Quickly established was the combination of haematoxylin, which stains nuclei blue, and eosin, a member of the aniline family, which stains cytoplasm, connective tissue and other extracellular substances pink or red.
Three years earlier, in February 1873, Camillo Golgi (1843 – 1926) announced the silver stain -- black reaction or reazione nera – which was to turn the Reticular Theory of Gerlach upside down. He noticed that when he immersed brain tissue, which had previously been fixed in potassium dichromate, in a weak solution of silver nitrate the nerve cells and their ‘elements’ were stained black . This staining technique was not easy to learn and did not immediately find favour with other neuro-scientists. But when Santiago Ramón y Cajal in 1886 got to hear of it he soon overcame the stain’s vagaries and went on to prove that the neurons of animals and humans were not joined together but were independent of one another -- the basis for the Neuron Doctrine -- and so earned for himself and Golgi places amongst the Nobel laureates.
The invention of microscopes dates from the early 1600s, although it had been known for a long time that a piece of spherically shaped glass magnified the object being looked at. Seneca (4 BC – 65 AD) wrote: ‘Letters, however minute and obscure, are seen larger and clearer through a glass bulb filled with water‘ . Roger Bacon (1214 – 1292) described a lens for reading which was ‘useful to old men and those having feeble sight. For they can see a letter, or anything small in sufficient size' .
It was probably amongst members of the Accademia dei Lincei that the idea first arose to make ‘a lens for looking closely at the smallest of objects’. Cesi was convinced that nature should be studied directly and not deduced from natural philosophy. Giovanni Faber (1574 – 1629) in a letter to Cesi dated 13 April 1625 named the instrument ‘microscopio’ -- derived from the Greek mikrόn (small) and skopeîn (to look at)  ; amongst other names it had up till then been called a ‘flea glass’. Gallileo Galilei (1564 – 1642), who had made a compound microscope consisting of three lenses housed in a tube made of cardboard, leather and wood which was inserted into an iron support with three curved legs, was recruited to the academy in 1611.
The Dutch draper-turned-scientist Anthonij van Leeuwenhoek (1632 – 1723)  is included in everybody’s list of early microscope makers, although he preferred to call his instrument a ‘simple magnifying-glass’. It was held up to the eye and consisted of a single biconvex lens held between two metal plates that also acted as the body of the instrument, a screw for adjusting the height of the object being examined (the lens did not move), and a skewer to impale the object to be examined and rotate it. In his life-time van Leeuwenhoek made more than 500 microscopes, more than half of them from silver, three from gold and the rest from brass, but only about ten have survived. He could blow glass and was a wizard at grinding and polishing glass. His best microscope had a lens that magnified 295x .
Compound microscopes containing lenses at opposite ends of an adjustable tube -- and sometimes within the tube -- were also made during this time. The origin of the invention, when and by whom, is uncertain, but is generally attributed to Zacharias Janssen (1580 – 1638). If the date of 1590 is correct, it is more likely that he improved on an istrument his spectacle-maker father had made earlier.
One of the best-known of the early compound microscopes was the one made by Robert Hooke (1635 – 1703). In the preface to his book Micrographia, or some physiological Descriptions of Minute Bodies  which was published in 1665, Hooke writes:
‘The Microscope, which for the most part I made use of, ..... the Tube ..... could be very much lengthened, as occasion required; this was contriv’d with three Glasses; a small Object Glass ....., a thinner Eye Glass ....., and a very deep one .....: this I made use of only when I had occasion to see much of an Object at once; .....’. (In ‘Observ. XVIII. Of the Schematisme or Texture of Cork, and of the Cells and pores of some such frothy Bodies he described what he saw when he looked at thin slices of cork with his microscope which had a magnification of 25x. He derived ‘cells’ from ‘cella’, the Latin for a small room, because what he saw reminded him of the small rooms monks live in. To be correct, what he saw were not cells, but the skeletons of dead cells).
Hooke later became acquainted with the work of van Leeuwenhoek through the Royal Society of London which was formally founded on 25 April 1663 when Charles II (1630 – 1685) accepted its Charter. The first secretary of the society, the Bremen-born Henry Oldenburg (1615 – 1677), corresponded with many of the outstanding philosophers and virtuosi of the day. One of them was Renier de Graaf (1641 – 1673), a physician and friend of fellow-townsman van Leeuwenhoek. In response to an account in the society’s journal – Philosophical Transactions -- of a new microscope made in Italy, de Graaf wrote to Oldenburg on 28 April 1673:
I am writing to tell you that a certain most ingenious person here, named Leewenhoeck, has devised microscopes which far surpass those which we have hitherto seen ..... The enclosed letter from him, wherein he describes certain things more accurately than previous authors, will afford you a sample of his work: ...... 
During the next fifty years van Leeuwenhoek wrote to the society several hundred letters (exact number uncertain), which were translated from his Delft version of Dutch into Latin and English, announcing his latest observations that permitted his biographer Clifford Dobell (1886 – 1949) to call him the ‘Father of Protozoology and Bacteriology’. In early 1680 Hooke, a Curator of the Society, wrote to van Leeuwenhoek expressing surprise that his name was not on the list of Fellows of the Society, an omission that was corrected on 8 February 1680.
In appreciation of what the Royal Society had meant to him, van Leeuwenhoek wrote the secretary a letter on 2 August 1701:
‘ I have a very little Cabinet ..... wherein lie inclosed 13 long and square little tins ..... in each of (which) lie two ground magnifying-glasses ..... every one of them ground by myself, and mounted in silver that I have extracted from the ore ..... This little cabinet ..... I have committed to my only daughter, bidding her to send it to You after my death, in acknowledgement of my gratitude for the honour I have enjoyed and received from Your Excellencies.’  Maria did so on 4 October 1723 the day after her father’s death from a suppurative lung illness at the age of 90. Sadly, sometime during the nineteenth century, one of the Fellows mislaid the collection which has not been seen since.
The simple microscopes were difficult to use. With both types of microscope, the compound more so than the simple, the images at higher magnifications tended to be blurred and spoilt by distracting colour aberrations because a spherical lens surface brings the light rays passing through the different parts of the lens to a focus at different points; in addition, the rays of the three primary colours of light -- red, blue and green -- are refracted differently. Joseph Jackson Lister (1786 – 1869), a wine merchant and father of the famous surgeon, is usually credited with an invention that nearly solved the problem. In 1830  he described the ‘achromatic doublet’, in which a convex lens made from crown glass was combined with a concave lens made from flint glass. Although others, such as John Dolland (1706 – 1761) in 1758, had done much the same, Lister found the solution by way of theory and experiment rather than by trial and error. It turned out that the best doublet was an ‘object-glass’ in which a plano-concave lens made from flint glass was cemented to a spherical lens made from crown glass. These lenses brought red and blue light to the same focus.
Lister did something else that contributed to the development of the microscope -- he encouraged Giovanni Battista Amici (1786 – 1868) to resume his work on achromatic microscopes. Amici was an engineer, professor of mathematics and astronomer of Modena, who had turned his attention to making ‘reflecting ‘ telescopes that used mirrors instead of lenses. In 1827 Amici travelled to London where he met Lister who owned a powerful achromatic microscope made in England. On 28 March the next year Lister wrote to Amici:
It is curious that achromatic glasses of short focus should have been produced ..... near the same time in Italy and England, independent of each other ...... I should be ful obliged to thu to inform me how long they have been employed by thu, whether any one on the continent before thu had succeeded in them, and also ..... to whom we are originally indebted for the important improvement of placing one before another in combination’. Amici replied on 12 May: ‘..... I can tell you that it was towards 1815 when I fitted my large-aperture Newtonian telescopes with achromatic eye-pieces ...... It was only in the year 1824 that I returned to this work with the certainty of greater success after reading the report made by Mr Fresnel (Augustin – Jean Fresnel, 1788 – 1827) to the Académie Royale des Sciences in Paris about the achromatic microscope of M. Selligue.It was from this latter that I took the fortunate idea of combining various achromatic object –lenses instead of constructing one of focal length equal to that of their combination ....... 
Amici was a prolific correspondent and his international relationships extended from America to Britain and through the universities of Europe to Moscow and St. Petersburg. Over a period of fifty years he made microscopes for most of the leading scientists of the time; Purkynĕ bought a small one in 1858.
The biographer of Amici  has even more praise for the man from Modena: ‘Amici’s most important contribution to the further improvement of the modern achromatic microscope was with the introduction of the immersion technique. He first used water, in 1847, and then different types of oils from the mid-1850s on’. Amici probably did not know that David Brewster (1781 – 1868) had by 1812 already done so and that Hooke had discussed the use of ‘mixtures of watery and oyly Liquors’ in Micrographia. If, historically speaking, Amici was not the first to attempt to enhance the magnifying power of the lens, he did much to promote it. During the 1860s and 70s the emphasis was on the production of water immersion lenses; the ones made by Edmund Hartnack (1826 – 1891), who worked with his microscope maker uncle George Oberhauser (1798 – 1868) in Paris, were judged to be the best .
The making of glass suitable for optical use proved to be difficult and took many years to perfect. Spectacles were invented in Italy in the thirteenth century but the available glass was opaque, and it was only in the 1600s that glass suitable for microscopes and telescopes were produced. The technique of making crown glass (formed when a hollow globe or ‘crown’ is formed by blowing into a pipe that had been dipped into a pot of molten glass) had been perfected for the making of window glass in France in the 1320s. Flint glass, containing nodules found in the chalk deposits of south east England, was produced in the 1670s and when George Ravenscroft (1632 – 1683) added lead oxide to the mixture a glass of good clarity was produced - the precursor of English lead crystal . In 1673 Ravenscroft set up a glass-making factory in London.
These early types of glass were inconsistent in quality, subject to chromatic aberration, and ‘crizzling’, an unstoppable process in which the glass became opaque and small cracks appeared on the surface. A solution had to be found and it turned out to be a simple one. In 1805 Pierre-Louis Guinand (1748 – 1824), a Swiss bell-pourer, replaced the wooden stirrers with ones made from clay which not only stirred the molten glass better but brought to the surface unwanted bubbles. When the word spread, he was hired by Joseph Utzschneider (1763 – 1840), a Bavarian entrepreneur who owned an optical institute. In 1807, together with a brilliant young man named Joseph Fraunhofer (1787 – 1826), he started to make flint glass of unprecedented homogeneity in the workshop of the Benediktbeuern Monastery, founded in 739. However the untimely death of Fraunhofer disrupted further progress and the knowledge of optical glass melting gradually died out in Germany .
The baton of quality glass making for microscope lenses now passed to England. Here the Government in 1824 decided to fund research into optical glass manufacture because British astronomers had come to realise that English telescopes were no longer superior to German or French ones. The man put in charge was Michael Faraday (1791 – 1867) who is better known for his discovery of electromagnetic rotation, the principle behind the electric motor. Faraday was familiar with Fraunhofer’s work. He also had friends in the platinum business. He stirred the molten glass in platinum trays using platinum stirrers and added grains of platinum to the mix because this helped to get rid of the tiresome unwanted bubbles. Although no less a person than Amici used Faraday glass to make lenses for notables, including one in 1838 for The Reverend Thomas Romney Robinson (1792 – 1882), Director of the Armagh Observatory in Ireland, Faraday lost interest in glassmaking because the quality of his product was no better than that made by cheaper methods .
Finally, in April 1845, the British Government decided to drop the debilitating excise duty that had hampered the growth of the English glass industry. Glass manufacture started to flourish in Birmingham in 1848 when Georges Bontemps (1799 – 1884), who had been the production manager of Feil and Guinand in Paris (a firm that had been set up by members of the Guinand family after the death of Fraunhofer), joined the Chance brothers, Lucas (1782 – 1865) and William (1788 – 1856). For some years after that the production of optical glass was centered in Paris and Birmingham.
In August 1877 physicist Ernst Abbe (1840 – 1905) reported he had found an oil which did not harden and damage the lens or the objective, as the natural cedar oil which was used up to that time did when exposed to air. It was in 1884 that he teamed up with glassmaker Otto Schott (1851 – 1935) and instrument maker Carl Zeiss (1816 – 1888) to found the famous Jenaer Glaswerke Schott und Genossen. Two years later, in 1886, Schott succeeded in making glass which corrected for all three primary colours of light and that year Zeiss began to market microscopes with what was called apochromatic objectives. Moreover, the resolution (definition) of these apochromatic lenses -- equal sharpness of several non-adjacent points in one field -- was superior to that of the achromatic lenses, an attribute that mattered more to the microscopists than magnification.
By the end of the nineteenth century reliable microscopes were made in America, France, Germany and the United Kingdom. One of the most sought after was that made by Ernest Leitz (1843 – 1920). Starting with serial number 1 in 1851 his company produced the microscope with serial number 50000 during 1899.
It is of interest that whereas the use of microscopes in Germany was mainly in the domain of the scientists, microscopy in Britain was also a social activity - much to the delight of the microscope makers - and the Microscopical Society of London was founded at a public meeting on 20 December 1839.
By the end of the nineteenth century Histology, the study of the microscopic anatomy of plants and animals, had emerged from its infancy to become a fully fledged member of the family of biological and medical sciences.
This came about because tremendous technical advances had been made during the century in the techniques that underpin histology, notably the introduction of staining and the perfection of the oil-immersion apochromatic lens, and because of the impact of scientists such as Johannes Müller who believed in the future of microscopy and taught his students how to use a microscope, and Albert Koelliker, the master collator, whose journal and books kept the scientific community abreast of the latest developments in the field of animal and human histology.
The article benefitted from the comments of Cape Town and overseas readers; I particularly appreciated the help of Alberto Meschiari and the suggestions of Sergio Musitelli. Mary Bock attended to the spelling and grammatical mistakes.
The costs incurred were covered by a legacy from Alwinus Bock (1905 – 1975).
Dr. J.C. de Villiers, Emeritus Professor of Neurosurgery, University of Cape Town recommends publication of this article.
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