layer, and the papilla', wliifh he surmised were
organs of touch. He elucidated the structure
of the liver, which Glisson (1597-1077),
professor at Cambridge, had already carefully
described, showing that it is an acinous gland of
peculiar construction, and, by tying the bile
duct, demonstrated that the bile is formed in
the liver and not in the gall-bladder.
As a consequence of the increase of the power of vision by the use of the microscope, the phenomena of fecundation and the development of the embryo began to receive attention. Spermatozoa were discovered in 1677 by a pupil of Leeuwenhoek. and De Graaf, discovering the ovisacs (Graafian follicles) about 1072, supposed them at first to be ova. Naboth, too, discovering the closed follicles of the neck of the uterus, supposed them to be ova (Ovula Nabothi). The ova of the lower vertebrates were, of course, well known, and the phenomena of their development were specially investigated by Malpighi. Van Horne, of Leyden, probably saw the human ovum in 1068, but it was not unmistakably recognized until Von Bar demonstrated it in 1827.
During the course of this investigation two schools arose — the Animalculists and the Ovists, that respectively maintained the superior efficacy of the male or female elements. Attempts were made to explain the transmission of hereditary qualities from parent to child. Aristotle, having studied the development of the egg, had declared that the embryo primitively consisted of simple, undifferentiated material, from which, by successive stages, the adult was formed (theory of post-formation or epigenesis). Opposed to this was another contention, that either the male or the female elements must possess in miniature all the organs of the adult (theory of preformation).
A further result of microscopic research was an enlarged view as to the distribution of living things. The discovery by Leeuwenhoek (1032- 172.'i) that organic infusions soon become replete with living forms when exposed to the air, led to the revival of the ancient notion of the spontaneous generation of living from non-living matter. This led to fanciful theories regarding fecundation that were not overthrown until Spallanzani (1729-99) showed that living forms do not develop in infusions that have been boiled and then excluded from the air, and that filtered seminal fluid has lost the power of impregnation. Following up the researches of Hartsoeker( 16.50- 172.5) he also demonstrated that ordinary air teems with living particles that enter the human body and pass into infusions. This doctrine was termed panspermatism, and developed afterward into the modern "germ theory." which has had a profound influence upon pathological anatniliy.
Tile following discoveries of this period may be briefly noted: Ole Worm (1588-1654), professor at Copenhagen. discovered the intercalary hones of the skull; Clopton Havers of England, in 1602, the Haversian canals and the intimate structure of bone; Hooke (1635-170."!), the primitive fibrilla? of muscle; Kerkring (1640-93), the valvulse conniventes of the small intestine; Winslow (1609-1700), of Paris, the foramen connecting the two cavities of the peritoneum; Douglas (1075-1742), of London, the recto-uterine pouch and several other features of the peritoneum and the abdominal wall.
The classification of animals by their anatomical structure, attempted first by Aristotle, was revived by several authors during the eighteenth century, and notably by Karl von Linng (Linnaeus) of Rashult, in Sweden (1707-78), who considered that each particular species was im- mutably established at the creation, man being placed' at the head in the order Primates. Buffon (1707-88), however, siipposed that varia- tions occur from changes of environment, and even hinted that all species may have origi- nated from a primitive common stock. This was afterward more boldly advocated by Lamarck (1744-1829), who was the first to maintain sys- tematically the mutability of species, and to look upon man as derived from a conunon stock with other organisms, conceiving that the ancestral record of all might be represented as a branching tree. To this was opposed the authority of the great comparative anatomist Cuvier ( 1769-1832), who caused these views to sink into obscurity for a time.
The controversy concerning the early develop- ment of the human body was renewed during this period. The weight of authority was over- whelmingly in favor of the theory of preforma- tion, notwithstanding the absurdities to which it committed its advocates. Its most earnest supporter was Haller (1708-77) (q.v.) , professor at Gottingen, a man of remarkable learning and indefatigable research, who did much to further exactitude in anatomical knowledge, and was the leading physiologist of his time. He made many anatomical discoveries in all parts of the body, and finally overthrew the doctrine of "animal spirits," which had ruled all investigations of the nervous system since the days of Hippocra- tes. He declared, however, that the body of our primitive mother Eve must have contained in miniature all individuals of the human race that had existed since her time and that were hereafter to exist! This was the less excusable, as Kaspar Friedrich Wolff, a young medical stu- dent, had published in 1759, as his graduation thesis, a remarkable essay, the Theoria Gcnera- tionis, in which he showed by accurate and con- clusive observations that the organs of the body are developed from membranous sheets (the blas- todermic membranes), and not from preformed rudiments. He even anticipated the cell-theory of the next century by stating that these mem- branes are themselves composed of globules (cells). Wolff made many other important in- vestigations, and his name has been perpetuated in that of the Wolffian body or primordial kid- ney. Such was the opposition with which his views were received that he was unable to obtain a professorship in Germany and went to Russia. It was not until Meckel called attention to his work in 1812 that his merits were fully recog- nized.
Aristotle, Eustachio, and Fallopio had surmised that the organs of the body might be composed of simpler elements: Boerhaave (1668- 1738) supposed that everything could be reduced to vessels and fibres; Haller (1708-77) classified structures according to their properties; Bonn (1738-1818) considered that membranes are the anatomical basis of structure. It remained, however, for Bichat (1771-1802) to establish clearly the doctrine that the body with all its organs is made up of a small number of simple tissues. This he did by an examination of their chemical, physical, and vital properties, dispensing wholly with the use of the microscope, then
