14 FUNCTIONAL INERTIA 



Here there is a definite insusceptibility to a series 

 of stimuli, a lack of correspondence between re- 

 sponses and stimuli. There are, in short, a number 

 of variables to be taken into account at the same 

 moment, viz., the two metabolic phases, the two 

 fundamental properties, and the stimuli. I follow 

 Verworn when he defines a stimulus as ' Every 

 change in the external vital conditions of an or- 

 ganism." Under this head constant stimuli, such 

 as condition of the blood, would not seem to be 

 included, but the definition should be enlarged to 

 admit of this, since blood is, for cells, one of their 

 external conditions, and for some cells it is a vary- 

 ing stimulus, for instance, as regards its varying 

 amounts of oxygen and of carbon dioxide. Stimuli 

 may be classified after Verworn * as 



(1) Those tending (a) to increase or (b) to decrease 

 anabolism ; + A and A and 



(2) Those tending to (a) increase or (b) to decrease 

 katabolism ; + K and K. 



In the appendix to this chapter a scheme of the 

 relationships between these various factors is given 

 in full. 



The principle involved may be stated thus : 

 Protoplasm in predominant anabolism on re- 

 ceiving a stimulus tending to cause it to change its 

 state' qualitatively (that is a positive katabolic 

 stimulus) will, if affectability be predominant, 

 begin to katabolise, but will, if functional inertia be 



* Vcrworn, " General Physiology," p. 357. (London : Macmillan, 

 1899.) t Ibid- P- 49- 



