PROCESSES OF IMMUNITY 165 



In accordance with the relatively slight effectiveness of this method, if 

 applied to homoiogenous skin grafts, it was found that splenectomy, which 

 causes a partial elimination of the reticulo-endothelial system, was ineffective 

 as far as improvement in the results of homoiogenous transplantation was 

 concerned. Also, in our experiments splenectomy did not weaken noticeably 

 the reactions of the host against homoiogenous transplants of thyroid and 

 other tissues. There still remains the method used by Rhoda Erdmann for 

 this purpose in amphibians, in experiments which we shall discuss subse- 

 quently. In general, as was to be expected on theoretical grounds, we may 

 then conclude that it has not been possible to change experimentally the 

 individuality differentials of tissues, although it may be possible to influence 

 the reactions of the host against strange differentials by certain experimental 

 procedures. As to the reason why the local reaction around transplanted 

 normal tissues does not reveal definite processes of immunity, under condi- 

 tions in which such effects can be demonstrated in the case of transplanted 

 embryonal or cancerous tissues, this may be due to the fact that both pieces 

 of embryonal and of tumor tissue, as a rule, grow much more rapidly after 

 transplantation and metabolize more actively than normal tissues and that 

 in all probability the former correspondingly give off larger amounts of 

 effective antigen. 



