ANIMAL BREEDING 209 



tion of cytost proves too much for their powers of 

 resistance. On this basis it is readily seen that when 

 such animals become pregnant their abilities to pro- 

 duce normal, healthy young must be seriously im- 

 paired. 



In captivity the guinea pig at best is not a very active 

 animal; hence it is easy to imagine that, due to its 

 limited muscular activity, it fails to stimulate anti- 

 cytost formation in the natural manner we have postu- 

 lated. From this brief discussion it should be clear 

 that the cytost injections employed in immunizing 

 such aged animals of poor fecundity must function 

 solely by stimulating the formation of anticytost in 

 quantity sufficient to overcome the effects of any cytost 

 liberated during the course of a pregnancy. In con- 

 sequence such animals are permitted to carry the de- 

 veloping fetus to term in a normal fashion. 



From the preceding discussion it appears likely 

 that much the same results could be achieved by sub- 

 jecting old, apparently sterile females to a course of 

 exercises of gradually increasing severity. So far as 

 the writer is aware this type of experiment has not 

 been investigated, but the results should prove of inter- 

 est. 



The conclusions reached above may be summarized 

 as follows: In order that domesticated and captive 

 wild animals may live a normal, healthy existence in 

 accordance with their birthright, every precaution 

 should be taken to inhibit the formation of cytost or 

 contact with cytost in excessive quantities. Oppor- 

 tunity must be offered to develop anticytost in a nor- 

 mal fashion, since this will protect the animals against 

 cytost intoxication. These ends may be achieved by 



