12 PROTOPLASMIC ACTION AND NERVOUS ACTION 

 SCOPE OF GENERAL PHYSIOLOGY 



The first four groups of characters appear to be 

 common to all forms of living matter; i.e., they are the 

 expressions of the general or fundamental properties 

 and activities of the living substance or protoplasm 

 wherever found. We class as ''living" all natural 

 systems exhibiting these properties in combination; and 

 general physiology has for its object the study of the 

 essential composition and activities of such systems. 



From this point of view the distinction between 

 animals and plants becomes one of minor importance. 

 This difference is essentially one of method of nutrition; 

 in plants the processes of constructive metabolism start 

 with more elementary and widely diffused materials 

 than in animals. A brief reference to the main points 

 of distinction seems relevant here, since it may assist 

 in defining the essential problem under consideration. 



It is evident that all organisms require for their 

 normal growth and activities the presence of energy- 

 yielding (chiefly oxidizable) materials in the protoplasm, 

 as well as materials for building up protoplasmic struc- 

 ture; the chief representatives of these two classes of 

 substances are, respectively, the carbohydrates and the 

 amino-acids. The main differences between plants and 

 animals relate to the methods by which these materials 

 are obtained or rendered available. In green plants 

 they are synthesized from simpler compounds which in 

 their unaltered state cannot serve as sources of energy — 

 CO2, salts, water. In animals the chief ''food " materials 

 are already complex compounds of high chemical 

 potential which are not synthesized in the organism 

 but are prepared outside of the latter (ultimately by 



