PROTECTION AGAINST HUNTING 3I7 



This table shows the importance and the extremely high signifi- 

 cance of the final yield, of tolerance: twice as many tolerant 

 animals and three times as many permanently tolerant animals 

 are obtaiaed in the series of animals which received facilitating 

 serum as compared to animals which received normal serum. 

 The probability that this result might have been due to chance is 

 less than lo"^. 



DISCUSSION 



The experimental results reported above deal mainly with 

 runting and protection against runting; with immunological 

 facilitation (enhancement phenomenon) and its application to 

 non-tumour tissues; with specific acquired tolerance and increased 

 rate to tolerance. The discussion will also deal successively with 

 these three questions. 



I. Runting and protection against runting 



A. What are the normal course and the mechanism of 

 rim ting ? 



In the experiments reported, runting occurred (in unprotected 

 animals) rather early — before day 7 — and reached its maximum 

 (as judged by death rate) around day 11 to 12, to decrease pro- 

 gressively, rapidly at the beginning (between day 14 and day 21) 

 and more slowly afterwards. It had not completely disappeared 

 (or, at least, it lethal consequences) on day 35. These facts 

 may have implications for the mechanism. of runting: they are 

 quite compatible with the generally accepted view that the basic 

 mechanism of runting is of the same nature as the mechanism of 

 homograft rejection. However, the following differences have 

 to be noted: the time of maximum severity of runting as 

 well as the end of its active phase are somewhat delayed as com- 

 pared to homograft rejection; furthermore its lethal consequences 

 can be observed from around day 5 to later than day 35. These 



