THE DEEPENING OF PHYSIOLOGY. 301 



gated, spindle-shaped, contractile cells arranged in a 

 ring around one of the openings, clearly represent- 

 ing the beginning of a sphincter muscle. Tissues are 

 aggregates of more or less similar cells with at least 

 one predominant function in common. 



Bichat. It was in 1801, at the threshold of our 

 period, that Xavier Bichat published his Anatomic 

 Generate which included an analysis of the body into 

 its component tissues muscular, nervous, glandu- 

 lar, connective, and so on, and furthermore a de- 

 velopment of the idea that the functions of organs 

 might be expressed in simpler terms, namely, in 

 terms of the properties of the tissues. We may take 

 this great work as the foundation-stone of the physiol- 

 ogy of tissues, the study of which has occupied no 

 small part of the energy of physiologists throughout 

 the century. The literature of research on muscular 

 or contractile tissue alone would fill a library. 

 Since it is necessary to restrict ourselves to one illus- 

 tration, we have chosen that which is perhaps most 

 generally interesting, the physiology of nervous 

 tissue. 



Nervous Tissue. Aristotle does not seem to have 

 had any idea of the physical basis of his own genius ; 

 he did not know the function of the brain, nor was 

 he clear as to difference between nerves and sinews. 

 The contrast between this primitive ignorance on 

 the part of one of the greatest minds the world has 

 known and the knowledge of the nervous system 

 possessed by physiologists to-day is remarkable, but 

 even more remarkable is the relative recentness of 

 that knowledge. Guesses and hints there may have 

 been, but the elementary distinction between sensory 

 and motor nerves was unknown a hundred years ago. 



At the beginning of the nineteenth century it was 



