282 THE ACTION OF THE LIVING CELL 



require re-investigation and extension. Thus, the ex- 

 periments upon immunity towards cytost and the 

 relationship of such immunity to natural resistance 

 and breeding might well be extended to larger num- 

 bers of animals and particularly to species other than 

 those used in our laboratory. 



The writer has not carried out any experiments with 

 invertebrate forms other than protozoans, but there 

 is every reason to suppose that in such animals cytost 

 must play a role similar to that in higher animals. In- 

 deed, Child (1915) has presented some evidence that 

 this is so in the case of planaria, for he states (page 

 66) : "There is no doubt that a relation exists between 

 the general metabolic condition of organisms and 

 their susceptibility to a large number of substances 

 which act as poisons, i.e., which in one way or another 

 make metabolism impossible." He further points out 

 that the action of such poisons resembles that of "cer- 

 tain soluble products of metabolism," and in so doing 

 comes close to the writer's concept that the toxic action 

 of many cellular poisons is largely due to their ability 

 to cause the liberation of cytost. Throughout his book 

 Child stresses the possible relationship between the 

 "soluble products of metabolism and the activity of 

 the animal." Thus (page 188) : "Fatigue, the de- 

 crease in rate of metabolism which follows continued 

 stimulation, is generally believed to be due to the 

 accumulation of toxic products of metabolism." And, 

 again: "Various metabolic intoxications are prob- 

 ably very similar in character . . ." 



In the chapter on the possible role of cytost in the 

 activities of the plant, we have presented evidence 

 that endocellular products which are liberated as a 



