The localization of all active properties in the cells gave renewed impetus to the study of the structure of these "elementary organisms." At first this structure was believed to be compara tively simple, the protoplasm of which the living substance is composed being apparently a struc tureless jelly haying peculiar physical and chem ical properties. Further advances toward per fecting the microscope and microscopic technique have shown this to be a mistake. That proto plasm has definite structure is now agreed by all; the details of the structure are still in dis pute. Eminent in this investigation were Carl Heitzmann of New York, Flemming of Kiel, and Biitsehli of Heidelberg. The phenomena of indi rect cell-division (karyokinrsis) were first con nectedly observed by Schneider in 1873, and have been especially investigated by Van Beneden, Boveri, Oscar Hertwig, and Bahl. The ulti mate constitution of the cell received a great deal of attention. Nlig,eli, in 1884, framed an hypothesis that protoplasm is composed of cer tain elementary units, termed mieella% whose combination produces its physical and vital properties much as a combination of molecules produces the physical properties of inorganic bodies. Similar, more widely developed theories were framed by De Vries, Hertwig, \Veismann, and others. Weisman]] attempts to explain the phenomena of heredity by supposing that bodily characters are caused by architectural peeuliari ties inherent in the original generative cells. This is, therefore, a reappearance of the theory of preformation so prevalent during the eighteenth century. Experiments by Ilertwig appear to have disproved Weismann's views. Great activity in the investigation of the structure of cells still continues. In America, Wilson of New York and 'Whitman of Chicago have made important contributions to our knowledge of this subject. Heitzmann, of New York, is well known for his attack upon the eell-theo•y as commonly taught, holding that the cells of the body are connected by minute threads of protoplasm; a theory that has recently been confirmed to a limited degree.
The great strides made in our general knowl edge of structure during the nineteenth century can only be briefly mentioned. The structure and development of bone was elucidated by Goodsir. Purkinje, Sharpey, and K011iker. the osteoblasts being discovered by Gegenbaur in 1864. The mechanism and development of joints were studied by Braune of Leipzig. Sutton of London, Dwight of Boston, and Bernays of St. Louis. The minute anatomy of muscle is still under consideration, and has been investigated by Krause, Ranvier, Cohnheim. and many others: Humphrey and Huxley (q.v.) in England and Gegenbaur in Germany have written on the gen eral morphology of the muscular system, and Gruber, Theile, Testut, and Ledouble have inves tigated muscular anomalies. The structure of the capillary blood vessels was first correctly demonstrated by Treviranus in 1836. The blood platelets or hematoblasts were by :Max Schultze in 1865. The lymphatics were investigated by K111liker, Ranvier, and Sappey.
In the nervous system the discoveries have been many and brilliant, completely revolution izing previous notions of its structure. Gratio let first showed the convolutionary pattern of the brain; Broca was the first to prove that certain motor faculties may be localized upon the cerebral cortex; a subject upon which extensive researches have been made by Fritsch and Hitzig, Ferrier and Horsley. Ehrenher;* of
Berlin appears to have been the first to describe, in 1833, the large cells of the cerebral cortex and of the spinal cord. The axis cylinder process of nerve cells was discovered by Wagner of Got tingen, Marshall Hall (q.v.) of London was the first to demonstrate reflex movements. Prochaska to discover the differential function of the ante rior and the posterior roots of the spinal nerves. By degeneration experiments instituted by Wal ler, by noting the myelination of nerve fibres as done by Flechsig. and by comparative studies it became possible to trace in the central nervous system the paths by which sensations are re ceived and motor influences discharged.
Improvements in technical methods finally made it possible to trace the processes of nerve cells to their minutest ramifications. This gave rise to the neurone theory. which holds that the nervous tissue is composed of independent cells or neurones that may ramify extensively, some of the ramifications passing into nerve fibres and forming their active conducting ele ments. This theory has been applied with suc cess to explain the architecture of the nervous system; a subject that is widely engrossing the minds of anatomists. and from which important results are expected in the future.
In the organs of special sense the new ideas of the constitution of the nervous system have elucidated many difficult problems. The anat omy of the ear has been studied by Riidinger, Helmholtz (q.v.) of Berlin, Retzius of Copenha gen. and Ayers of Cincinnati. The organ of Corti was discovered by the Marchese di Corti in 1851. Schwalbe of Strassburg first saw the taste-buds of the tongue in 1867, Meissner and Wagner the tactile corpuscles in 1852. The teeth have been a special object of research with the American anatomists Ryder, Osborn. and Cope, especially with reference to the mechanics of their development.
The researches of American anatomists have borne fruit in other fields. W. E. Horner of Philadelphia discovered the tensor tarsi or deep layer of the o•bieularis palpebrarum, and Wil liam Clay Wallace of New York was the first to show the real nature of the ciliary muscle (1835). ft is to Henry J. Bigelow, of Harvard University, that we owe the first accurate de scription of the ilio-femoral ligament of the hip joint and its application to the reduction of dis locations. His work on the hip, published in 1869. completely revolutionized surgical practice in this matter. It should not be forgotten, how ever, that Reid, of Rochester, N. Y., had previ ously, in 1851, shown many of the facts after ward more completely stated by Bigelow. In the realm of comparative anatomy, and espe cially of paleontology, Joseph Leidy, 0. C. Marsh, Harrison Allen, and Edward D. Cope have done much to extend the fame of American science.
BIBLIOGRAPHY. Among the recent works on Bibliography. Among the recent works on human descriptive anatomy may be mentioned: Quain. Gray. and Morris, in English; Testut and Poirier, in French; Gegenbaur and Rauber, in German. Bardeleben is editing a large work in German. in eight volumes, by various authors. On topographical anatomy, McClellan and Treves, in English: Tillaux, in French. and Hyrtl, Ger lach. and Merkel, in German. are good works. There is no satisfactory treatise on the history of anatomy. A fairly complete resume is found in Volume I. of The Reference Handbook of Medi cal t'.4eicnees (second edition, New York, 1900).