210 M. F. GUYER 



normal mating vigor, but no young resulted from the union. 

 On March 27th, his semen was again examined microscopically. 

 Spermatozoa were more plentiful than at the last examination 

 and some of them showed considerable activity. Neither 

 numbers nor activity were back to normal, however. His 

 mating to 84 on this date yielded six young. On May 13th he 

 was bred to 6A2. His semen, though normal in quantity, was 

 almost devoid of spermatozoa. The few which were present 

 were wholly immobile. No young resulted from this mating. 

 On June 1st he was mated to 31 A3 without issue. His semen 

 was almost free from spermatozoa. Here and there an immobile 

 one was visible and very rarely a mobile one. June 12th, condi- 

 tions were practically the same. A mating to 7A1 yielded no 

 young. 



This male (4A7) was then left with a female from June 12th 

 until the middle of October, when he was killed for a study of his 

 testes. Although he copulated with the female from time to 

 time, no young were born. His semen was examined again 

 July 3rd and seemed to be wholly devoid of spermatozoa. Upon 

 removal, the testes were found to be somewhat smaller than usual 

 for a rabbit of his size and somewhat flabby. Upon sectioning, 

 however, no differences could be discerned between his semmif- 

 erous tubules and those of a normal male rabbit. The usual 

 series of spermatogonia, spermatocytes, spermatids, and sperma- 

 tozoa in all stages of transformation were in evidence. More- 

 over, some of the spermatozoa teased out of the epididymis and 

 examined in normal saline solution were feebly motile, though 

 most of them were inactive. In the case of this particular indi- 

 vidual, at least, the sterilizing effects of the spermatotoxic 

 serum apparently did not extend back beyond the mature 

 spermatozoa. 



From time to time tests were also made of the spermatotoxic 

 action in vitro of the sensitized fowl-serum. For example, on 

 March 3rd and March 4th the serum of fowl no. 1 was tested. 

 Hanging-drop preparations were made of: 1) normal rabbit 

 spermatozoa in normal saline solution; 2) normal rabbit sperma- 

 tozoa in normal fowl serum, and, 3) normal rabbit spermatozoa 



