72 PHYSIOLOGY 



the body. The heat produced in the organs is not only 

 conducted through the body but conveyed by currents of 

 the everywhere circulating blood. Just as the heating 

 of a building by hot-water pipes is partly a mechanical 

 problem, so in the warming of the body there is a 

 mechanical factor, namely the circulation of the blood. 



The uses of the body which physiology earliest 

 glimpsed were those of mechanical design. The study 

 of bodily form, being relatively simple, was early 

 prosecuted. It was easy by dissection of the dead and 

 examination of the shapes of bones and muscles to infer 

 in outline what would be the mechanical adjustments 

 of those parts in life. Up to the sixteenth century 

 physiology followed merely that crude method, chemistry 

 and physics hardly as yet existing. The form of 

 the organs of the body is significant chiefly where 

 they are machinery for the application of mechanical 

 powers. But the greater part of the corporeal machinery 

 is not mechanical but has its purpose in processes, 

 chemical, thermal, electrical, &c. Even with regard to 

 muscle the study of its gross form can say nothing on 

 the fundamental question, ' How is its force developed ?' 

 The form of the liver or the pancreas tells us nothing of 

 the function of those great chemical organs ; their form 

 fits into the space-conditions of the abdomen. Study of 

 the gross form of the brain has never shed light on the 

 functions of that organ, nor is it likely that it ever will. 



But in the middle of the seventeenth century there 

 came to physiology one discovery of a mechanical kind of 

 importance. Besides the ordinary muscles such as move 

 the bones there is one muscle which is hollow. Its cavity 

 opens into the tubes of the arteries and receives opening 

 into itself the tubes of the great veins. This muscle is the 

 heart. Harvey by watching it at work and by experiments 



