Chapter VIII 



INVESTIGATIONS CONCERNING 

 NATURAL RESISTANCE 



In the last chapter we were led to certain specula- 

 tions regarding natural resistance and the role played 

 by cytost in this important aspect of normal physi- 

 ology. Let us now consider the results of various ex- 

 periments which have been made by the writer in an 

 attempt to test the validity of his conclusions con- 

 cerning natural resistance. For convenience, such 

 experiments may be divided into three groups: 

 (a) those dealing with the susceptibility to cytost as 

 evidenced by the ease of the induction of shock by 

 the injection of that substance; (b) wound healing; 

 and (c) experiments concerning the breeding of cap- 

 tive animals. In each of these groups we shall for the 

 present limit our discussion to animals whose natural 

 resistance has been raised by a preliminary series of 

 cytost injections. 



It will be remembered that when small graded 

 doses of cytost are injected every few days for some 

 weeks into laboratory animals, these animals undergo 

 a progressive increase in weight and apparent well- 

 being. If such injections are discontinued before the 

 animals suffer a decline as shown in the graph on 



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