398 , DISCUSSION 



conceivably stimulate lymphocytopoiesis in either host-type or donor- 

 type lymphoid cells. 



Barrett: Do you have any data yet on whether the thymocytes do 

 repopulate ? 



Miller: Not yet. We are hoping to obtain these data by performing 

 cytological analyses on cells dividing in the spleen of thymectomized 

 and thymus-grafted mice of appropriate strains. 



Krohn: Speaking for endocrinologists, I am delighted that we have at 

 last found a function for the thymus. 



In relation to the thyroid changes following thymectomy, is it possible 

 that operative trauma might interfere with the thyroid ? 



Miller: When we do sham thymectomy we employ the same opera- 

 tive technique as for total thymectomy, except, of course, that the 

 thymic lobes are not sucked out. Radioactive iodine uptake by the 

 thyroids of sham-thymectomized mice appeared to be within the 

 normal range. 



G. Klein: If I understood it correctly, you could re-estabHsh the re- 

 activity of the thymectomized mouse by implanting an isologous 

 thymus in some cases. 



Miller: In most cases. 



G. Klein: Did you try homologous, or shall we say, allogeneic 

 thymus ? 



Miller: I have no results on that. 



G. Klein: It would be interesting, if it succeeded, to see whether the 

 reactivity would correspond to the donor or the host-type cell. 



Voisin: Did you study the globulins in the sera of the animals? 



Miller: I am trying to do electrophoresis of these sera now. 



Billingham: Have you tried thymectomy at different ages? 



Miller: Not in sufficient numbers to be able to estabUsh exactly at 

 what age thymectomy is still associated with impairment of homo- 

 graft immunity. 



Billingham: What is the latest age at which thymectomy will give 

 evidence of graft tolerance ? 



Miller: We don't get it after 2 weeks; I shouldn't think we would 

 get it after 7 days. 



Brent: Is it possible to re-equip these mice with reactivity by using 

 disrupted thymus cells — extracts of one kind or another ? 



