8 Mr. J. C. Mottram and Dr. S. Russ. Susceptibility and 



written on the slides, which were then tabulated. The results are shown 

 graphically in fig. 7. 



Fig. 7. 



The finding of an occasional normal animal, or one bearing a progressively 

 growing tumour with a very high lymphocyte and plasma-cell content, does 

 not, however, rule out the possibility that in such cases these cells may be 

 playing some part in what may still be called immunity. Eeference to 

 Table I shows that a small number of animals, exhibiting all the outward 

 signs of susceptibility, simultaneously exhibit an immunity to the graft, for 

 they resist re-inoculation. 



The question remained, therefore, as to whether these few animals 

 corresponded with the small proportion of their class, giving a high 

 lymphocyte and plasma-cell count. This was put to the test direct in the 

 following way : A batch of normal rats was taken, and a small portion of 

 their spleens removed ; they were then given an inoculation into the right 

 axilla. 



The animals grew tumours, of which frequent records were kept ; when at 

 least four measurements upon each rat had been made, selection was made of 

 those which had progressive tumours (Type 1) ; a further portion of their 

 spleens was then removed, and their lymphocyte and plasma-cell content 

 again determined. 



It was found that the majority, 19 out of 22, of the rats growing 



