292 ON GROWTH AND OVERGROWTH 



corresponds to and makes up for the loss of substance brought 

 about by this increased activity, for so long is there no tendency 

 towards cell multiplication. It, however, may happen that 

 after stimulation the amount of absorption and assimilation 

 may be in excess of the needs of the cell. We have, in short, 

 to recognize the existence of the principle of inertia. 



Inertia, physically speaking, is one of the properties of 

 matter in general. Now, just as according to physical termino- 

 logy there are two kinds of inertia inertia of matter at rest 

 (or inertia of mass) and the inertia of matter in motion (or 

 momentum) so in relation to the protoplasm of the cell we notice 

 the same kinds of inertia in evidence. As Dr. Harris points out, 1 

 protoplasm which is at rest cannot be instantly caused to change 

 that state to respond to stimuli. We have the familiar latent 

 period, and numerous examples can be given of that functional 

 inertia which corresponds with the inertia of movement (momen- 

 tum), " the inertia that makes the wheel rotate long after you 

 have ceased to spin it." The isolated heart of the frog will 

 continue to beat long after its removal from the body. Hairs 

 continue to grow after the death of the body ; indeed, all cases 

 of organs and tissues continuing to perform functions after their 

 blood supply has been cut off are cases of functional inertia. 



And coming now to the immediate problem before us, it may 

 be said that active katabolism, with the active performance of 

 function, leads to corresponding increased anabolism, and that 

 if by nervous or other mechanism the performance of function 

 be arrested, the absorption of nutrition and assimilative processes 

 may still continue for a time. If there be continued access of 

 nutriment, this, according to the above principle, is liable to 

 continue over and above the needs of the cell. In other words, 

 there is a liability for reserve material to be heaped up in the 

 nucleus and body of the cell. It is, I would suggest, under these 

 conditions that proliferation may replace functional activity. 

 If the cell be not called upon to perform its normal functions, be 

 not called upon to work after previous stimulation has led to 

 increased absorption and anabolism, that cell is in a favourable 

 condition to divert its energies from function to proliferation. 



In this connexion I would point out that we are forced to 

 recognize that the stimulus for the performance of special function 

 1 D. F. Harris, British Medical Journal, September 15, 1900, p. 741. 



