276 THE ACTION OF THE LIVING CELL 



is commonly ascribed to individual variations in re- 

 sistance or susceptibility. 



These variations in resistance to cytost injections, 

 however, are especially interesting since they repre- 

 sent a resistance to a product of the animal's own cells, 

 and suggest that, other things being equal, an animal's 

 health and well-being may depend upon his resistance 

 to the toxic products resulting from the activities of 

 his body cells. 



This line of thought led to two series of investiga- 

 tions concerned respectively with the toxic effects of 

 sublethal quantities of cytost, and the stimulation of 

 natural resistance to that substance. These have been 

 discussed at length in previous chapters, where it was 

 shown that, depending upon both the quantity of cy- 

 tost injected, and the number of injections, an animal 

 may be caused to suffer an actual decline in weight and 

 health, or stimulated so that it gains in weight and 

 general appearance. 



The latter result appears to depend upon a general 

 stimulation of the metabolism of the body cells of the 

 animal, as well as the production of an increased tol- 

 erance for cytost. The apparent stimulation of metab- 

 olism may really be due to the latter, for it is con- 

 ceivable that in the case of an animal having a low 

 resistance to cytost, the accumulation of the latter in 

 its body fluids may impair the functioning of the body 

 cells so that their activities are below normal. If, on 

 the other hand, the animal's resistance to cytost is 

 raised by a course of immunizing injections, such im- 

 pairment of function is largely removed and the 

 growth of the body cells assumes a more normal 

 course. This aspect of the problem is one worthy of 



