NATURAL RESISTANCE 



175 



a combination of factors which early brings about 

 their death. Obviously, then, such conditions may be 

 utilized as a rather severe test of our ability to raise an 

 animal's natural resistance by injections of cytost. 



6C. 



Chickens 



ECGSX 



JAN. Feb. Mar. Apr. May Ju.n. Jul. 



Figure 13. Graphs showing the effects of cytost injections upon 

 the monthly egg production of hens. The ordinates represent the 

 percentage of the hens which laid eggs each day and the abscissae 

 represent the time after the beginning of the experiment. Curve A 

 refers to the hens stimulated by cytost injections; curve B represents 

 the hens in which a decline was caused by cytost injections; and 

 curve C the control flock. (From Turck, 1923.) 



Kittens born of normal mothers were divided into 

 two groups. The members of one group were in- 

 jected with a cat anticytost serum which had been 

 prepared as above described, while no attempt was 

 made to immunize the individuals of the other group. 

 All the kittens were then placed in cages which had 

 been sprayed with a potent cytost preparation. All 



