144 HOWARD, MICHIE AND WOODRUFF 



Three of the graft-bearing A mice were injected intraperi- 

 toneally with 60-90 million axillary lymph node cells from A mice 

 which had recently rejected (A x CBA) skin grafts. Three other 

 graft-bearing A mice were selected as controls. For a longtime no 

 effect was observed, so that the presumption of tolerance seemed 

 to be in serious doubt. At the end of the sixth week, however, 

 the grafts of all three treated animals began to show signs of 

 disrepair, followed, in two cases, by hair loss and scarring a few 

 days later. The third lingered on, displaying focal eczematous 

 lesions beneath a thinning crop of hair. Unhappily for the decisive- 

 ness of the experiment, one of the three control mice began to 

 show a similar lingering reaction not long after the onset of 

 rejection in the three treated animals. Were it not for this circum- 

 stance we would feel reasonably sure of our diagnosis of the graft- 

 bearing mice as tolerant animals, in the strict sense of central 

 inhibition. As it is, while regarding this explanation as over- 

 whelmingly likely, we recognize the need for further reinforce- 

 ment of this link in our chain of evidence. The long delay 

 preceding the first signs of adoptive breakdown can, by hindsight, 

 be regarded as unsurprising. In contrast with the adoptive test as 

 applied to classically tolerant animals, in which the overwhelming 

 mass of lymphoid tissue is of host origin (Michie, Woodruff and 

 Zeiss, 1 961), our transplanted lymph node cells had to establish 

 themselves in lymphoid masses which, as we have seen, consisted 

 mainly of donor (A x CBA)Ficells. The latter might be expected 

 to present an absorptive screen, which the adoptive cells must 

 first overwhelm before being able fully to deploy against the 

 grafted skin. 



Ittittiiinization of newborn mice 



If transplantation tolerance is inducible in adults by massive 

 administration of cells carrying donor-strain antigen, it seems 

 possible that the variable which decides, at any given age, whether 



