CHAPTER III 



ELEMENTARY VITAL PHENOMENA 



WHAT is called life is a series of vital phenomena very un- 

 equal in importance. As regards most of the activities that con- 

 stitute the daily life of mankind, some are composed of elementary 

 phenomena, and some are secondary results of elementary pheno- 

 mena. Even those that are apparently simple and direct, such as 

 the circulation of the blood and respiration, are not elementary. 

 The elementary phenomena are the contraction of the heart 

 and the respiratory muscles, which secondarily accomplish the 

 circulation of the blood and the exchange of air in the lungs ; for 

 muscle-contraction cannot be reduced to the activity of other 

 elements, it is the direct expression of the life of those cells in 

 which it appears. If we wish to become acquainted with the 

 elementary vital phenomena, we must go back to the cells in which 

 they appear. 



If all complex activities and secondary phenomena be traced 

 back to the elementary vital phenomena that lie at their founda- 

 tion, three great groups of the latter are found, which in some 

 form are peculiar to all living substance, to every cell ; these are 

 the phenomena associated with changes of substance, of form, and 

 of energy. All living substance without exception, so long as it 

 lives, shows continual changes of its material, alterations of its 

 form, and transformations of its energy ; and all vital phenomena 

 whatsoever, when resolved into their elements, may be placed in 

 one or more of these three great groups. In this chapter we shall 

 endeavour to obtain a comprehensive view of vital phenomena by 

 recording the facts, and shall leave to a later chapter the reduction 

 of them to mechanical causes. 



I. THE PHENOMENA OF METABOLISM 



A. THE INGESTION OF SUBSTANCES 



' Nourishing," in the widest sense, signifies the whole process 

 involved in the taking-in of food-stuffs from the environment. In 



