INTRODUCTION 5 



of the body. The body may therefore be regarded as composed of myriads of cell units, organ- 

 ized into units of gradually increasing complexity, very much as a social community is composed 

 of individuals organized into trades, municipalities, etc. 



Most of the individual tissues can be recognized bj^ their gross appearance. In fact, the 

 principal tissues were first demonstrated by Bichat through skilful dis.section, maceration, 'etc., 

 and without the aid of the microscope. The cellular structure of the ti.ssues was later discovered 

 by Schwann in 1839. 



Each cell (fig. 3) is composed of a material called protoplasm, a viscid substance variable in 

 appearance and exceedingly complex in chemical composition. It readily breaks down into sim- 

 pler chemical compounds, whereby energy (chiefly in the form of heat and mechanical energy) is 

 liberated. It has also the power of absorbing nutritive material to build up and replace what 

 was lost. Its decomposition results from stimuli of various kinds, and hence it is said to be 

 irritable. The mechanical energy which it liberates is manifested by its contractility, especially 

 in the muscle cells. It excretes the waste products produced by its decomposition. Each cell 

 has the power, under favourable conditions, of reproducing itself by division. Protoplasm pre- 

 sents, in short, all the forms of activity manifested by the body as a whole; and, indeed, the ac- 

 tivities of the body are the sum of the activities of its constituent cells. 



In the protoplasm of each cell is a specially differentiated portion, the nucleus (fig. 3). The 

 nucleus plays an important part in regulating the activities of the cytoplasm, the general proto- 

 plasm of the cell body. The nucleus differs from the cytoplasm both structurally and chem- 

 ically, and contains a very important substance, chromatin, which during cell division is aggre- 

 gated into a definite number of masses called chromosomes. The cytoplasm of actively growing 

 ceUs also contains the archoplasm and centrosome, structures of importance in the process of cell 

 division. Further details concerning the cells and tissues m.ay be found in the text-books of 

 cytology and histology. 



In earlier days Human Anatomy was almost entirely a descriptive science, but little atten- 

 tion being paid to the significance of structure, except in so far as it could be con-elated with 

 physiological phenomena as they were at the time understood. In recent years attention has 

 been largely paid to the morphology of the human body and much valuable information as to 

 the meaning of the structure and relations of the various organs has resulted. Since the form 

 and structure of the body are the final result of a series of complicated developmental changes, 

 the science of Embryology has greatly contributed to our present knowledge of human INIor- 

 phology; and, accordingly, a brief sketch of some of the more important phases of morphogenesis 

 wiU form a fitting introduction to the study of the adult. 



References. — General: For looking up the literature upon any anatomical 

 topic, the best guide is the "Jahresbericht ueber die Fortschritte der Anatomic 

 und Entwicklungsgeschichte/' which contains classified titles and brief abstracts 

 of the more important papers in gross anatomy, histology and embryology. 

 Other useful aids are the ''Zentralblatt fuer normale Anatomie," the "Index 

 Medicus" and the catalogue of the Surgeon Genera 's Library of the War Dep't. 

 (Washington, D. C). The latter two contain titles only, but cover the whole 

 field of medicine. The "Concilium Bibliographicum" also provides a conveni- 

 ent card-index system of references for the biological sciences, including 

 Anatomy. 



For nomenclature: His, Archiv f. Anat., 1895 (BNA system); Barker, Ana- 

 tomical Nomenclature. Cells and tissues: Wilson, The Cell; Hertwig, Zelle und 

 Gewebe (also English transl.) ; Schaefer, Microscopic Anatomj^ (in Quain's 

 Anatomy, 11th ed.); Heidenhain, Plasma und Zelle. 



