EXPERIMENTS WITH CYTOST 113 



periments, seven of the ten cats which had been kept 

 in the laboratory were still healthy and vigorous. 



In order to follow more closely the rate of increase 

 in weight of animals so treated a series of cats was in- 

 jected every four days with 0.25 cc. of homologous 

 cytost extract and the weights of the animals were de- 

 termined at the time of each injection. In figure 11 

 data from three representative experiments have been 

 plotted. In each instance it will be noted that the 

 cytost injections led to a marked increase in weight up 

 until the time of the tenth or twelfth injection, after 

 which the animal's weight fell, only to rise again to 

 a value which was maintained despite further injec- 

 tions of cytost. 



In these experiments, the small quantity of cytost 

 injected first causes an increase in weight, due pre- 

 sumably to increased metabolic activity; then a re- 

 action sets in which causes a loss in weight although 

 the original level is not reached. This is apparently 

 due to tissue damage caused by an excess of cytost, 

 for post-mortem examination of some of these animals 

 disclosed evidences of chronic involvement of the 

 lungs, and gastritis. However, such damage is slight 

 and appears to be readily overcome by the animal, 

 which then regains its lost weight. The final rise in 

 weight may perhaps be attributed to the production 

 of antibodies against cytost. It seems probable that it 

 is the presence in these animals of the latter, which we 

 may call anticytost, which prevents the development 

 of pronounced pathological changes such as those 

 found in other experiments previously cited. It is in- 

 teresting to contrast this series of experiments with 

 those summarized in Table IX on page 1 03. In the lat- 



