2 INTRODUCTION 



lated by their structure, it is dependent primarily on 

 living matter itself. The functions of human beings 

 are therefore not unique. They are but highly developed 

 characteristics common to all animals. 



We do not tat and breathe because we have a certain 

 number of bones and a definite arrangement of muscles, 

 though the manner of eating and breathing may be in- 

 fluenced by this arrangement. We might as well expect 

 a steam engine to go because it has a certain number of 

 wheels and pistons. These may determine the manner 

 of its going, but without the steam it remains still. A 

 dead man has the same gross anatomy as a living man. 

 If anatomy were a determining cause of activity the 

 functions of the body would not stop when death occurs. 



Exactly what the difference between living and dead 

 matter may be we do not know, but we do know the way 

 in which living matter manifests the fact that it is alive ; 

 and we know that wherever it is found, in the simplest 

 animal or in the most complex, these manifestations are 

 the same. The point of departure in the study of physi- 

 ology should therefore be the activity of the living sub- 

 stance. In studying this activity and the causes that 

 control it we find that physiology is related to physics 

 and chemistry and that this relation is more vital than 

 its relation to anatomy. Through physics and chemistry 

 we may explain the activity of living matter; through 

 anatomy we explain nothing but accidental modifica- 

 tions of its activity. 



The human body, though the most complex and won- 

 derfully efficient machine in existence, has in common 

 with the simplest animals and plants only the functions 



