CHAPTEE I 



GENERAL PHYSIOLOGICAL METHOD 



1. PHYSICAL, CHEMICAL, AND HISTOLOGICAL METHODS 



PHYSIOLOGY makes use of all the modern aids to research in natural 

 science. We have not infrequently to employ the finest instruments of pre- 

 cision and the highest mathematical analysis. The physiology of the two 

 highest sense organs, the eye and the ear, has progressed so far that every 

 fact which relates not to our own perceptions and interpretations, hut to the 

 purely physical conditions of their origin, can be treated with a discrimination 

 and exactness of experimentation which place this portion of physiology on a 

 plane with the most exact of all natural sciences, namely, physics. The same 

 holds, for the most part also, in the general physiology of cross-striated muscle 

 and nerve. Here electrical science and several other branches of physics have 

 found wide application. 



The study of the circulation of the blood presents an extraordinarily 

 complicated problem in hydraulics; the study of equilibrium and locomotion 

 of the body is to be treated from a purely mechanical point of view; in the 

 discussion of the respiratory exchange of gases in the lungs and in the tissues 

 physiology turns to account both theoretically and experimentally the physical 

 theory of gases; and the doctrine of heat regulation is based naturally on 

 the physical theory of heat. In short, almost every division of physics has 

 some direct bearing upon our study of the functions of the body. 



In the same way chemistry is of far-reaching importance in physiological 

 research. The chemical nature of the substances contained in or formed in 

 the animal body is one of the first things to be considered. Besides this, 

 chemical physiology has to investigate also the changes which the ingested 

 substances undergo in the vital processes of the body. 



Microscopical investigation furnishes us valuable data with regard to the 

 activity of the cells, and histological methods have therefore very wide appli- 

 cation in physiology. 



The physiology of the sense organs and of the central nervous system 

 stands in very close relation with psychology and the theory of knowledge, 

 or to put it more strongly, a thoroughgoing study of this branch of physiology 

 is impossible without a knowledge of these sciences. 



Finally, physiology must take into account also the discoveries of pathology 

 and of pharmaco dynamics. For however the functions of the body are influ- 

 enced by the different abnormal changes, or by poisons, they are not altered 

 in nature; and the study of these changes must evidently throw light on the 

 normal processes. 

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