This early worker was noted for the variety of his investigations rather than for the depths of his learning. Amongst the so-called Observations, in his book are many that are not connected with microscopic work. The following are interesting and, in the curious old book Micrographia, there are an extraordinary number of well executed illustrations. Early in his book Hooke compares various man-made objects, such as a razor edge, the point of a needle and a piece of cloth, with various natural objects, and always to the detriment of the former. He examined Foraminifera with his microscope, and was probably the first man to draw these beautiful little creatures. Petrified wood and charcoal also came under his notice. When he studied cork, he observed that it was made up of “little boxes or cells,” and the name cell has survived to this day despite the fact that it is by no means an appropriate term. That Hooke’s knowledge was not very deep is shown by the fact that he presumed cork to be a fungus growing on the bark of trees.
Many of the objects we have described in our pages were described and illustrated by Hooke more than two hundred years ago. The sea mat, despite his accurate observations, he mistook for a seaweed, as many later naturalists have done. The stinging hairs of nettle he made out in every detail. Fish scales, bee stings and birds’ feathers all came under his notice. The foot of a fly he described with wonderful accuracy; the scales of a butterfly’s wing and the head of a fly were all studied and described in detail. On the life history of the gnat he made many blunders, but he saved his reputation by remarkable observations upon the Chelifer, a curious parasite of the fly which we mention in our pages, and upon the silver fish, a little creature which frequents sugar and starch. Neither of these organisms had been described before. Fleas, lice, vinegar-eels and spiders were also studied by this indefatigable worker, a worthy collection indeed, but Hooke, like others of his time, was an observer first and foremost. As a methodical, scientific worker he was of little account.
Living about the same time as Hooke, the celebrated Italian, Malpighi, laid the foundations of much of our present-day knowledge of plant structure. Various romantic stories have been told concerning certain imaginary events which led Malpighi to take up the study of plant structure, but the scientist himself refuted these picturesque stories. Suffice it to say that his book on the subject, Anatome Plantarum, though imperfect in many respects and, as might be conjectured in so early a work, often inaccurate, contains a large number of astonishingly good drawings; many of the original drawings, by the way, executed in red chalk, are in the possession of the Royal Society.
It is interesting to note that this botanist compared the falling of leaves to the shedding of an insect’s skin, in this respect at any rate he had advanced no further than Aristotle, who compared leaf-fall to the moulting of a bird. On the other hand, the Italian was the first scientist to describe the pores (stomata) of leaves, though he never discovered that they occurred on all leaves. He, first of all men, showed that nectar was formed by the flower and not transferred thence from other sources as had previously been believed; he too explained accurately for the first time the process of germination in the seed. It was not alone as a botanist, however, that Malpighi was celebrated. He elucidated the various changes which take place during the hatching of an egg; he was the first man to give an accurate account of the structure of an insect, and this he did in his work on the Anatomy of the Silkworm. Using a simple microscope for his investigations, he contracted an eye affliction during this period from which he suffered more or less severely all the rest of his life. He discovered the breathing tubes of insects and that when they are covered with grease the insect will die “in the time that one can say the Lord’s Prayer”; the heart, the silk glands, the development of wings and legs were all discovered for the first time by this untiring worker, aided by his simple microscope.
Pages could be filled with accounts of Malpighi’s other scientific work on the structure of the lung, the liver and kidney, the life of the liver fluke and a hundred and one other subjects. Though undoubtedly a great and clever microscopist, the general estimate seems to be that his work had little influence upon the scientific world. The main reason is that he was ahead of his time; men of the day concluded, for instance, that in his Anatomy of Plants he had said the last word on the subject, that there was no more to be learned. An English worker, Nehemiah Grew, carried the Italian scientist’s studies of plant structure a little further and his Anatomy of Plants contains many new and often accurate observations. His studies also led him to discover the structure of the ridges and sweat pores of the human hand, in fact Grew may be looked upon as the originator of the study of finger prints.
A Dutchman, Jan Jacobz Swammerdam by name, and a contemporary of Grew, was undoubtedly the most accurate observer amongst these old-time microscopists. Despite ill health, his enthusiasm was unbounded, and a friend wrote concerning him: “Swammerdam’s labours were superhuman. Through the day he observed incessantly, and at night described and drew what he had seen. By six o’clock in the morning in summer he began to find enough light to enable him to trace the minutiæ of natural objects. He was hard at work till noon, in full sunlight, and bareheaded, so as not to obstruct the light, and his head steamed with profuse sweat. His eyes, by reason of the blaze of light, became so weakened that he could not observe minute objects in the afternoon, for his eyes were weary.” If only for the fact that the Dutchman made clear the processes involved in the transformations of insects, his name would be famous. He described the structure and habits of the hive bees, male, female and drone with wonderful accuracy, and illustrated his work with plates which “would do credit to the most skilful anatomists of any age.” Swammerdam was sarcastic at times; he had shown that the facets of a bee’s eye are six-sided and, as so commonly happened in those days, some naturalists jumped to a conclusion, in this case that the fact explained the six-sidedness of the cells in the honey comb. By the same reasoning Swammerdam remarked that men, having round pupils, should build round houses. It is not only for his study of the minute structure of insects that this microscopist is noted, he worked upon the tadpole and the snail. He it was who discovered the red blood corpuscles of the frog, and he described his discovery in the following terms: “In the blood I perceived the serum in which floated an immense number of rounded particles, possessing the shape of, as it were, a flat oval, but nevertheless wholly regular. These particles seemed, however, to contain within themselves the humour[1] of other particles. When they were looked at sideways, they resembled transparent rods, as it were, and many other figures, according, no doubt, to the different ways in which they were rolled about in the serum of the blood. I remarked besides that the colour of the objects was the paler the more highly they were magnified by means of the microscope.” Of the snail he made a number of strikingly accurate studies, in all of which he was aided by his lenses, so that it is the more remarkable that he considered snails to be insects.
Leeuwenhoek, another Dutchman, [we have already mentioned in our previous chapter]. He of all men brought the simple microscope to its highest state of development. His instruments were one of the sights of Holland, and many eminent personages made a point of seeing them. Though he had not the advantage of any scientific training and spoke no other language than his own, he made some remarkable additions to the scientific knowledge of the time. Like Hooke, he was not a methodical worker, he was impelled by an unbounded curiosity. “When we are inclined to disparage Leeuwenhoek’s hasty methods it is well to recollect that he initiated biological inquiries of the greatest interest, e.g., the parthenogenesis of aphids and the revivification of dried microscopic organisms, while he gave the first notices, or the first worth mention, of rotifers, Hydra, infusorians, yeast cells and bacteria.”
We may here explain the meaning of the term “parthenogenesis of aphids.” The female aphids or green flies are able to bring forth generation after generation during the first two-thirds or so of each year without the assistance of males. This form of increase, which by the way accounts for the extraordinary numbers of green fly, is known as parthenogenesis.
Leeuwenhoek thought that no one but himself could use his lenses properly, in consequence, when he sent any interesting object to a friend for him to examine, a lens was always affixed in place so that the object could be seen to the best advantage. He gave a set of his lenses and objects to the Royal Society, and described his gift as “a small black cabinet, lackered and gilded, which has five little drawers in it, wherein are contained thirteen long and square tin boxes, covered with black leather. In each of these boxes are two ground microscopes, in all six and twenty; which I did grind myself, and set in silver; and most of the silver was what I had extracted from minerals, and separated from the gold that was mixed with it; and an account of each glass goes along with them.”
Kircher, [whose work we mentioned in our last chapter], was overwhelmed with the notion that various living creatures are generated from non-living matter. Fleas, for example, he was certain, came from dirt, and it remained for Leeuwenhoek to prove that they arise from eggs and grubs, in the manner now so well understood.