ENDOCRINE FUNCTION OF THE THYMUS GLAND 329 



Control tests with normal rabbit serum and different kinds of 

 extracts were tried carefully. Precipitation took place in some 

 test-tubes, but in a decidedly slighter degree than with the 

 immune serum. 



b. Test of the antitestis serum in vivo 



Two litters of the same age, five and six individuals in each 

 litter, were used to test the antitestis serum in vivo (experiment 

 series nos. VIII and IX). About one half of the rats were in- 

 jected subcutaneously with the antitestis serum, 0.3 cc. to 0.5 

 cc. at each injection, with five to six days' interval, while the other 

 half, the controls, were injected with the normal rabbit serum. 

 They were put under the same experimental conditions, each litter 

 being in one cage and weighed almost every day until killed. 

 The examination was made in one series at thirty-four days, in 

 the other at forty-six days after the last or fifth injection. 

 Several organs were removed, examined, weighed, and fixed in 

 Bouin's solution for histological examination. In the male special 

 attention was paid to the sperm cells, which were carefully 

 studied microscopically after a quick operation. 



Neither the graphs nor the tests just described reveal any 

 particular difference between' the test and the control rats, nor 

 is there any marked difference in the weight of the thymus. 

 Table 7 will give the general features of the results. 



Average percentage''^ of tJie observed weight of the thymus compared with the iveight 

 calculated on the body weight or on the age {Donaldson, '15) of the test and control 

 animals of the series nos. VII and IX 



Observed weight 

 Percentage = Calculated weight ^ ^^^ ^'' '''''' 



