The remarkable group of investigators that made the glory of the Royal Society extended its researches into the sciences of life. The omnipresent Hooke demonstrated experimentally what Sir Kenelm Digby—that “arrant mountebank,” as Evelyn called him 57—had already pointed out: that plants need air for their life. He sowed lettuce seed in soil under the open sky, and, at the same time, similar seed in similar soil in a vacuum chamber; the first grew an inch and a half in eight days, the other not at all. Hooke identified the part of the air used up in combustion with the part used up in plant and animal respiration, and described this used part as nitrous in character (1665). He showed that animals which had stopped breathing could be kept alive by blowing air into their lungs with bellows. He discovered the cellular structure of living tissue, and invented the term cell for its organic constituents. Through his microscope the members of the Society saw with delight the cells of cork, whereof, Hooke estimated, one cubic inch contained 1,200,000,000 cells. He studied the histology of insects and plants, and gave novel drawings of them in his Micrographia. Hooke was always on the verge of ranking with Galileo and Newton.
Another member of the society, John Ray, shared in giving its modern form to the science of botany. He was the son of a blacksmith, but he made his way to Cambridge, became a fellow of Trinity College, and was ordained an Anglican priest. Like Boyle, he gave his devotion to religion as well as to science. Because he would not sign the Act of Uniformity (1662) pledging nonresistance to Charles II, he resigned his fellowship, and set out with his pupil Francis Willughby on a tour of Europe to gather data for a systematic description of the animal and plant kingdoms. Willughby undertook the zoology, but died after completing the sections on birds and fishes. In 1670 Ray issued a Catalogus Plantarum Angliae, which became the frame of English botany. Helped by the improved terminology and classification established in 1678 by Joachim Jungius, Ray proposed a Methodus Plantarum Nova (1682), which divided all flowering plants into dicotyledons and monocotyledons according to their having two seed leaves or only one. He completed his great task in one of the chefs-d’oeuvre of modern science, the massive three-volume Historia Generalis Plantarum (1682–1704), which described 18,625 species of plants. Ray was the first to use the word species in its biological sense, as a group of organisms derived from similar parents and capable of reproducing their kind. This definition, and the later classification by Linnaeus (1751), set the stage for the controversy over the origin and mutability of species. Meanwhile Ray edited Willughby’s manuscripts on ichthyology and ornithology, and added a Synopsis Methodica Animalium Quadrupedum (1693), providing for modern zoology the first really scientific classification of animals. 58 Order was Ray’s first law.
Even in antiquity botanists had recognized that some plants might be termed female because they bore fruit, and others male because they did not, and Theophrastus, in the third century before Christ, had observed that the female date palm produces fruit only if the dust of the male date palm has been shaken over it; but these ideas had been almost forgotten. In 1682 Nehemiah Grew, of the Royal Society, gave a new charm to flowers by definitely affirming the sexuality of plants. Studying plant tissues under the microscope, he noted the pores in the upper surface of leaves, and suggested that leaves are organs of respiration. Flowers he described as organs of reproduction: the pistils as female, the stamens as male, the pollen as seed. He mistakenly assumed that all plants are hermaphrodites, uniting male and female structures in one organism. In 1691 Rudolf Camerarius, professor of botany at Tubingen, definitely proved the sexuality of plants by showing that they would bear no fruit after the removal of their anthers—the pollen-containing part of the stamens.
On the same day (December 7, 1671) that the Royal Society of London received Grew’s first essay (The Anatomy of Vegetables Begun) it received also a manuscript from Marcello Malpighi of Bologna. The Society published it (1675) as Anatomes Plantarum Idea; the use of Latin was still facilitating the international of science. Malpighi divided with Grew the honor of establishing the histology of plants, but his major contribution was to zoology. In 1676 Mariotte, by chemically analyzing the residue of plants and the soil in which they had grown, showed that they absorb nutritive elements in the water that they suck from the earth. Neither Mariotte nor Grew nor Malpighi recognized the power of plants to take nourishment from the air; but the processes of nutrition and reproduction now discovered were a vast advance upon Aristotle’s vague explanation of plant growth by the expansive ambitions of the “vegetable soul.”
An old and popular notion received in 1668 the first of several shocks when Francesco Redi of Arezzo published his Esperienze intorno alia generazione degli insetti—experiments tending to disprove abiogenesis, or the spontaneous generation of living organisms from nonliving matter. Until the second half of the seventeenth century it was almost universally believed (William Harvey an outstanding exception) that minute animals and plants could be generated in dirt or slime, and especially in decaying flesh; so Shakespeare spoke of “the sun breeding maggots in dead dogs.” 59 Redi showed that maggots did not form on meat that was protected from insects, but did form on meat exposed. He formulated his conclusion in the phrase Omne vivum ex ovo—“Every living thing comes from an egg or a seed.” When protozoa were discovered, the argument for abiogenesis was revived; Spallanzani answered it in 1767, and Pasteur again in 1861.
The discovery of those single-celled organisms which were later termed protozoa was the major contribution of this age to zoology. Anton van Leeuwenhoek was a Dutchman of Delft, but he reported through the Royal Society at London his scientific results through forty of his ninetyone years. Coming of a family of rich brewers, he was able to accept employments that offered him more leisure than pay, and he gave himself with fascinated pertinacity to studying the new world of life revealed by the microscope. He had 247 of these instruments, most of them made by himself, and his laboratory sparkled with 419 lenses, some of which may have been ground by Spinoza, who had been born in the same year (1632) and the same land as he. Peter the Great, when in Delft in 1698, made it a point to peer through Leeuwenhoek’s microscopes. When (1675) the scientist turned one of these to the study of some rain water that had fallen into a pot a few days before, he was astonished to see “little animals appearing to me ten thousand times less than those represented by Mons. Swammerdam and by him called water fleas or water lice, which may be perceived in the water with the naked eye”; 60 and he proceeded to describe an organism that we now recognize as the bell animalcule (Vorticella). This was apparently the earliest description of a protozoon. In 1683 Leeuwenhoek discovered still tinier organisms—bacteria. He found them first on his own teeth, “though my teeth,” he protested, “are kept usually very clean”; and he startled some neighbors by examining their spittle and showing them, under the microscope, “a great many living creatures” therein. 61 In 1677 he discovered spermatozoa in semen. He marveled at nature’s profuse equipment for reproduction: in a small quantity of human semen he estimated a thousand spermatozoa; and he calculated that in the milt of a single codfish there were 150 billion sperm—more than ten times the number of inhabitants that the earth would contain if all the land were as thickly populated as the Netherlands.
Jan Swammerdam was five years younger than Leeuwenhoek, but preceded him by forty-three years to the grave; he was a man of nerves, passions, ailments, and fluctuating purposes, who stopped his scientific work at thirty-six and burned himself out at forty-three (1680). He was intended for the ministry, but abandoned theology for medicine. Having secured his medical degree, he devoted himself to anatomy. He became enamored of bees, and especially of their intestines; he spent his days in dissecting them, his nights in reporting and illustrating his findings. When he had finished his classic treatise on bees (1673) he broke down physically; soon thereafter he gave up science as too worldly a pursuit, and returned to religion. Fiftyseven years after his death his manuscripts were collected and published as Biblia Naturae, the Bible of nature. This contained, in remarkably exact detail, the life history of a dozen typical insects, including the May fly and the honey bee, and microscopic studies of the squid, the snail, the clam, and the frog. Here, too, were descriptions of the experiments by which Swammerdam proved that muscles in tissues cut off from an animal’s body could be made to contract by stimulation of the connecting nerve. Like Redi he rejected abiogenesis; he went further, and showed that instead of decaying flesh producing minute organisms, it is these that produce decay in organic matter. In his brief career Swammerdam founded modern entomology, and established himself as one of the most accurate observers in the history of science. His return from science to religion personified the hesitation of modern man between a search for truth that smiles at hope and a retreat to hopes that shy from truth.