22 FUNCTIONAL INERTIA 



supply." ' In heterauxesis, induced by lateral 

 stimulation, by gravity, light or heat, there is a 

 latent period before the geotropic, heliotropic or 

 thermotropic curvatures begin to be manifested. 

 This latent period that of anabolic inertia may 

 be of any length from a few minutes for geotropism 

 to a few hours for thermotropism." . . . "To wound- 

 stimuli, growing as well as adult organs exhibit non- 

 responsiveness in varying amount. Thus, trau- 

 matropic curvature in growing roots is only mani- 

 fested after a latent period of anabolic inertia of half 

 an hour or so, and this period may be artificially 

 lengthened to as much as eight days. Here, as in 

 other cases where a sense-organ has been demon- 

 strated, transmission time has to be deducted from 

 the (total) latent period to get the duration of the 

 anabolic phase." 



Now with regard to latent period, it is on this 

 view virtually a refractory period, so that the 

 refractory period of cardiac muscle is its latent 

 period of contraction. I find this is the view taken 

 by Professor Gregor Brodie * in discussing the 

 inability to tetanise the heart : it is the inertial 

 phase that is the cause of this inability. The heart 

 cannot be hurried beyond a certain pace : tetanising 

 stimuli no doubt accelerate its rhythm a little, but 

 a limit is soon reached. Professor Brodie remarks 

 that as tetanic stimulation is continued, the cardiac 

 refractory period is lengthened, i.e., the inertia is 



* T. Gregor Brodie, " Essentials of Experimental Physiology," 

 p. in. (Longmans.) 



