8O RALPH S. LILLIE. 



familiar to all; and essentially similar conditions are found in 

 other tissues and organs. Functional hypertrophy following 

 excessive activity, and regression or atrophy following prolonged 

 inactivity, are both well-known phenomena; for example, com- 

 pensatory hypertrophy in heart muscle is a frequent result of 

 valvular lesions, and one kidney increases in size if the other is 

 removed. In general it would appear that any physiological 

 function can reach and preserve its highest perfection only 

 through continual repetition; and this very condition implies 

 that decline must follow inactivity if the latter is prolonged 

 beyond a norm. And since every function has some organized 

 structure as its correlate, the same considerations apply to what- 

 ever structures are concerned in the function in question. The 

 modifications which the central nervous system undergoes in 

 association with the process of learning afford instances of an 

 essentially similar kind; practise facilitates the repetition of any 

 complex voluntary action, i. e., perfects the structural and other 

 adjustments underlying the function; 1 while any accomplish- 

 ment, intellectual or other, declines with disuse. These ex- 

 amples may suffice to illustrate the general principle under con- 

 sideration. It seems clear that the physico-chemical mech- 

 anisms whatever their nature may be controlling functional 

 activity are in some intimate relation to those determining growth. 

 The above facts seem to imply that both classes of physiological 

 processes are simultaneously and equally under the control of 

 some more general set of conditions characteristic of living sub- 

 stance in general. We shall now consider this possibility in 

 more detail. 



Claude Bernard has pointed out how essential it is in any 

 living system if the system is to continue to exist that there 

 should be a relation of interdependence between the processes 

 of destruction and of repair, of such a kind that any destructive 

 or dissimilatory process sets in motion automatically the con- 

 trary process of repair. 2 All functional activity involves break- 



1 This is the basis of the phenomenon of memory. Hering has discussed briefly 

 the relations between memory and heredity in his well-known address on "Memory 

 as a General Function of Organized Matter," Vienna Academy, 1870; English 

 translation by Open Court Publishing Company, Chicago, 1897. 



2 "Lecons sur les phenomenes de la vie," Vol. I, Chapter 3. 



