a very imperfect instrunent. He applied these
views to the elucidation of the anatomy of
oj'gans att'ected b3' disease, a subject previously
studied by Morgagni (1G82-1771) and by John
Hunter (1728-93). Bichat's death, at the early
age of thirty-one, caused by imprudent exposure
in the dissecting-room, was a great loss to ana-
tomical science.
The science of chemistry had now advanced to a ]ioint where it could throw much light upon the composition of the animal body. Four great organic gases had been discovered: carbon di- oxide ( imperfectly known to Van Helmont in 1640) by Black in 1757, hydrogen by Cavendish in 17GG, nitrogen by Rutherford in 1772, oxygen by Priestley in 1774. Lavoisier (1743-94) showed the importance of all these gases to the animal economy. Fourcroy (1755-1809) was practically the first to investigate the composi- tion of organic products.
The investigation of the human body by so many competent and careful observers gave a new scope to anatomical teaching. It was seen that no proper knowledge of anatomy or surgery could be obtained without the use of the cadaver. At first, legal enactments and social ostracism were directed against those who practiced dissec- tion; but on the Continent of Europe public dis- sections were frequently held from the time of Vesalius, and as men of commanding intellect like Malpighi, Stensen, Boerhaave, Morgagni, Haller, Bichat, Hunter, and many otliers devoted themselves to the pursuit of anatomy, the social stigma was gradually removed. On the Conti- nent, laws were early enacted by which the bodies of prisoners and paupers were turned over for anatomical purposes. In Great Britain, how- ever, this was not done, and bodies were quite commonly obtained by robbing graves. Wlien, in 1S27, the Universitj' of Edinburgh made dissection compulsory, and this example was fol- lowed by the other large schools in the United Kingdom, the demand for cadavers became so great that it was practically impossible to sup- ply it without breaking the law. A set of ruf- fians known as "resurrectionists" became estab- lished in every large city, and no cemetery was safe from their depredations. In Edinburgh two scoundrels named Burke and Hare made a business of enticing poor and friendless persons into their haunts, smothering them, and selling their bodies to the medical schools for dissection. Similar cases were those of Bishop and Williams in London. A remedy for this was found in an anatomy act passed in 1832. which legalized dis- section, and authorized the use of available material under certain restrictions.
Improvements in the microscope made about 1824 gave a new impetus to research. Earlier observers (Hooke, KiOo; Grew and Malpighi, 1671; Wolff, 1759) had dimly surmised that organic forms were composed of elementary units, but Schwann, in 1839, was the first to demonstrate this for animals in a satisfactory manner. Observations by Von JIolil, Purkinje, Leydig, KoUiker, Virchow. and Max Schultze soon placed this fact beyond cavil, and thus was established the celebrated cell-theory, which de- clared all organized beings to be composed of essentially similar minute units. This led to great improvements in microscopical technique and the investigation of the chemical properties of cells. Stilling invented section cutting in 1842; Gerlach, carmine staining in 1S58; Reck- linghausen, silver staining in 1800; Waldeyer, double staining with aniline dyes in 1803. and Golgi, bichromate of silver staining in 1873. With the establishment of the cell-tlieory came some remarkable generalizations, which have had a profound effect upon anatomy. Accord- ing to the views advanced by Herbert Spencer, Milne-Edwards, and others, the human body is to be considered as a cell-community, in which the laws of division of labor and of differentia- tion that in human society cause specialization into trades, classes, and employments are ap- plied to the morphological units, the cells. Cer- tain cells become specialized for special func- tions, and thus are produced the diversified forms of the tissues of the body.
Another remarkable result of the improved methods of investigation was, that the body of animals was shown to be developed from a single cell, the ovum. The series of phases by which this astonishing change is effected occupied the attention of many investigators, notably Pander, Von Bar, who established the theory of the germinal laj'ers or blastodermic membranes; Serres, who pointed out the great similarity between the successive phases of the embryo and J the series of animal forms now existent on the m globe, and a great number of others in all civ- ilized nations. Many details of this wonderful series of changes have yet to be supplied, but the general features of it are now firmly established. A great impulse was also given to Pathological Anatomy. The phenomena of disease were now traced to the cells, and a knowledge of their ana- tomical changes was found to be essential. In 1836 Cagniard de la Tour discovered the yeast plant, and many fanciful theories of fermenta- tion and disease were overtluown. Pasteur (1822-1895) demonstrated that all fermentations and putrefactions are caused by minute spores that swarm in ordinary air. The parasitic character of many disorders now became evident, and the foundation was laid for modern aseptic surgery. See Hi.stology and Pathology. It was not until 1859 that the knowledge hitli- erto obtained was fully applied to the elucidation of the causes of bodily structure. In that year Charles Darwin published the Origin of Species, and followed it in 1871 with The Descent of Man. These works advanced beyond the position of Lamarck, in that they showed an efficient cause for the cumulative variation of structure among organisms. This is the "struggle for existence"' which results in the extinction of those forms not suited to the environment. Unlike the speculations of many previous writers, these views were advanced with extreme caution and supported by a great number of careful observations. They were acce]ited by a large body of naturalists, and caused a renewal of activity in anatomy and the allied sciences. It became evident that to fully understand the structure of man it was necessary to ascertain the laws of development both in the embryo and in the animals from which the human stock may be derived. Comparative Anatomy, Embryology', and Paleontolog;^' thvrs became powerful coadjutors to Human Anatomy.
The importance of the study of the varieties of man now became recognized. Previous workers in this field were Camper (1722-89), the inventor of the facial angle; Blumenbach (1752-1840), who divided mankind into five races; and Retzius (179C-18G0), the inventor of the cephalic
