240 HILDEMANN, LINSCOTT AND MORLINO 



Our choice of the strain combination C57BL/6 adult cells-> 

 A/Jax newborns or C57BL/A F^ newborns was based on the 

 finding by BiUingham and Brent (1959) that C57->A was one of 

 the few combinations that led to 100 per cent deaths from runt 

 disease when 4-10 miUion C57 spleen cells were injected intra- 

 venously. However, it is probable that neither of their sublines 

 was isogenic with our C57BL/6 (H-2^) and A(H-2^) lines obtained 

 from the Roscoe B. Jackson Laboratory, Bar Harbor. 



Newborn mice were injected by the intracardiac route using 

 the ingenious technique devised by Grazer (1958). This approach 

 has the advantage of prompt systemic dispersion of the inoculated 

 cells. No magnification is required and there are no post-injection 

 haematomas. The newborn mouse will easily tolerate the injection 

 of 0-05 ml. of cell suspension and there is usually no leakage after 

 withdrawal of the 30-gauge needle. 



To assess the mitotic potentialities of the peripheral blood 

 lymphocyte preparations, the tritiated thymidine-radioauto- 

 graphic techniques of Bond and co-workers (1958) and Gavosto, 

 Maraini and Pileri (i960) were employed. Tritiated thymidine 

 was added to cells suspended in plasma-Hank's solution (i : i) 

 in amounts of 0*25 (Jic to i*o [jlc per 10^ cells per millilitre and 

 incubated at 3 7° with gentle agitation. Samples were removed at 

 intervals up to three hours, centrifuged to concentrate the cells, 

 and smears were then made. The smears were fixed either in 

 Carnoy's solution, or in methanol followed by iN-HCl to remove 

 any acid-soluble radioactivity. Shdes were washed well with tap 

 water, and stripping film (Kodak Ltd., London, AR 10 fme-grain 

 film) was applied in a humid atmosphere. Slides were incubated 

 in the dark for periods ranging from one week to six weeks. 

 The fdm was then developed and the slides stained with Wright's 

 stain. 



The pattern of development of transplantation disease in neo- 

 natal mice was studied quantitatively by the weight-gain assay of 

 Russell (i960) and by the liver-spleen enlargement assay of 



