DISCUSSION 267 



organ weight in an animal whose other tissues have lost weight? 

 Therefore it would not be comparable to splenic enlargement. 



Hildemann: The indices are relative to the organ weights of littermate 

 controls. The enlargement of some of the organs is terrific; it is really 

 remarkable that an animal can have such a low body weight and still 

 have such very large organ weights. We have two opposing factors here. 



EichwaU: But the organ is not enlarged; the rest of the body is 

 decreased in size. 



Hildemann: No, I disagree. We compare each organ with the same 

 organ of littermate controls, or the body weight with the body weight 

 of Httermates. 



EichwaU: Per 10 g. ? 



Hildemann: The calculated indices are quotients representing the 

 body weight or relative organ weight per 100 g. body weight over the 

 mean of the respective weights of two httermate controls. 



Woodruff: There is an important element in your argument that you 

 mentioned briefly that Td like more details about: you said that you 

 got high tolerance easily with foetal hver. I think this is very crucial 

 because until you came to that point in your paper, it seemed to me that 

 the failure to get tolerance could be explained as a pecuUarity of the 

 C57 mouse as donor or, in more general terms, as Dr. Simonsen men- 

 tioned, that it is difficult to produce tolerance with a combination of 

 donor and host which is commonly associated with severe runt disease. 

 This hypothesis seemed to be borne out by some experiments which 

 Dr. Michie and I performed some years ago in which we tried, but 

 completely failed, to make CBA mice tolerant of C57BL homografts 

 by injecting (CBAXC57) F^ spleen cells in the neonatal period. I 

 would be interested to know therefore how strong your evidence is 

 that it is easy to produce tolerance with C57BL foetal liver. 



Silvers: How many cells did you use? 



Hildemann: We got prolonged but not permanent tolerance with as 

 few as I • 5 milHon viable, nucleated foetal liver cells, and the tolerance was 

 based on survival of female C57BL/6 skin homografts for 60 days or 

 more. We got no acute rejections whatsoever and the majority of 

 grafts survived beyond 80 days. 



Michie: As a rider to the experiment that Prof. Woodruff has men- 

 tioned, although we couldn't induce any tolerance with 10 or more 



