With the establishment of the cell-theory 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 sells. 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 Mir, who established the theory of the germinal layers or blastodermic membranes; Serres, who pointed out the great similarity between the successive phases of the embryo and the series of animal forms now existent on the 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 1S36 Cagniard de la Tour discovered the yeast plant, and many fanciful theories of fermenta tion and disease were overthrown. Pasteur (1822-1895) demonstrated that all fermenta tions and pntrefactions are caused by minute spores that swarm in ordinary air. The para sitic character of many disorders now became evident, and the foundation was laid for modern aseptic surgery. See HisTotouv and PATHOLOGY.
It was not. until 1859 that the knowledge hith erto obtained was fully applied to the elucida tion of the causes of bodily structure. In that year Charles Darwin published the Origin of Species, and followed it in 1S71 with The De scent 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 envi ronment. Unlike the speculations of many pre vious writers, these views were advanced with extreme caution and supported by a great num ber of careful observations. They were accepted by a large body of naturalists, and caused a renewal of activity in anatomy and the allied sciences. It became evident that to fully under stand the structure of man it was necessary to ascertain the laws of development both in the embryo and in the animals from which the
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human stock may be derived. Comparative Anatomy, Embryology, and Paleontology thus be came powerful coadjutors to Human Anatomy.
The importance of the study of the varieties of man now became recognized. Previous work ers in this field were Camper (1722-S9), the in ventor of the facial angle; Blumenbach (1752 1840) , who divided mankind into five races; and Retzius (1796-1860), the inventor of the cephalic index for comparing crania. In America Sam uel G. Alorton became widely known by his great collection of crania. now in the Academy of Nat ural Sciences in Philadelphia. His Crania Amer icana and Crania ,Egyptiaea were important con tributions. His collections were, in 1856, de scribed and commented on by another anatomist. J. Aitken Aleig,s, who did much to establish the modern methods of the mensuration of the skull. No account of this period is complete without a reference to the work of Jeffries Wyman, of Harvard University. who was a man of great erudition and philosophical insight. As a mor phologist he had no superior among the anato mists of his day. Ile was the first to describe the arrangement of the bony spirals in the neck of the human femur, and to contrast it with that in those animals that do not assume the erect posture. He gave the first scientific de scription of the anatomy of the gorilla, and wrote on symmetry and homology in the limbs, on the vertebral theory of the skull, on terato logical subjects, on spontaneous generation, and on the anatomy of the Hottentot. The question of the unity or diversity of origin of the human race, which was closely connected with the origin of species, excited considerable attention in America about the middle of the nineteenth century. J. C. Nott and George R. Gliddon were the joint authors of two important works on this subject, entitled Types of Mankind and Indigenous Races of the Earth. This study was greatly stimulated by the discovery of human remains in strata belonging to previous geologic epochs, particularly at Engis and Spy in Bel gium, Neanderthal near Dusseldorf, at many places in France, and in South America. Fi nally the prediction of Morton. made forty years before, was verified by Dubois, who found, in the Eoeene strata of Java, fossil remains of a remarkable transition form between apes and man (1S90-95). This department of anatomy was greatly advanced by the zeal and energy of Paul Broca (1824-S0) of Paris, who system atized the methods in vogue, and invented many new ones for the examination of the human body.