CHAPTER V 



THE VITAL FUNCTIONS 



THE activities of a living organism which together make 

 up what we call its " life " may be conveniently con- 

 sidered under separate heads which are often called 

 " the vital functions." These divisions are to some 

 extent artificial, for one process passes into another, 

 and others are the results of the interaction of more 

 than one. We must always remember that what we call 

 the different life processes in reality form a continuous 

 whole. They are all expressions of the activity of 

 protoplasm in maintaining its physico-chemical equi- 

 librium in relation to its surroundings, though these 

 expressions are strikingly different in different organisms. 

 The " vital functions " are those expressions which 

 we can seize upon and give names to, and which are 

 of essentially the same nature in all living organisms, 

 whether animals or plants, simple or complex. 



We must carefully distinguish between the activity 

 of the organism as a whole and the activity of the 

 protoplasm itself, though the former depends of course 

 directly upon the latter, since protoplasm is the only 

 living part of an organism. This distinction is least 

 evident when the whole body of the organism, as in the 

 amoeba, consists solely of a naked mass of protoplasm. 

 In multicellular organisms, the relations of the whole 

 body to its surroundings are necessarily different from 

 the relations of the protoplasm of each living cell to 



