2 GENERAL ZOOLOGY 



attempts to reach such an understanding by assuming, as a work- 

 ing hypothesis, that life had its origin in natural rather than 

 supernatural causes and that it is therefore a phenomenon sub- 

 ject to the laws and principles of the basic sciences of physics and 

 chemistry. The ultimate goal of the scientific searcher — the 

 explanation of living phenomena in terms of scientific phe- 

 nomena — is still far from achievement; in fact it may be impos- 

 sible of achievement for the reason that life may involve some 

 factor or principle outside the realm of chemistry and physics. 

 However that may be, the broad, general, and practical lines of 

 approach to the study of the problem of life are relatively few in 

 number and may be summarized as follows : 



1. The study of the physical and chemical properties of proto- 

 plasm, the living matter of which organisms are composed and 

 with which life is always associated. Such work falls largely in 

 the province of the biochemist who deals with protoplasm as a 

 substance to be analyzed by appropriate chemical laboratory 

 methods. 



2. The study of the morphology or the form and structure of 

 animals and plants. This is commonly subdivided into: 



a. Gross anatomy, which is morphological study in its 

 broad aspects, carried on by the dissection of the bodies of 

 animals. In gross anatomical studies the analysis of structure is 

 made with the unaided eye, i.e., without the use of a magnifying 



lens. 



b. Microscopic anatomy or histology, the study of the more 

 minute structure of tissues and organs, in which special prepara- 

 tions are made for examination and study under the microscope. 



c. Cytology, the study of the finest structural details of 

 cells, the morphological units of which tissues and organs are 

 composed; the microscopic study of protoplasm as distinguished 

 from histology, which is primarily concerned with the study 

 of the structure and arrangement of cells. 



d. Embryology, the study of the development of an 

 organism; the study of embryogeny. In embryology the 

 methods of dissection and microscopic study are both used. 



3. Physiology, the study of the functions of organs considered 

 separately and in relation to the organism as a whole. It deals 

 with the process of waste and repair in living things, food, and the 

 sources and transformation of energy. It also has to do with the 



