182 Dr. Bashford, Mr. Murray, and Dr. Cramer. [Dec. 10, 



The blood of other nearly allied animals (rat, rabbit, guinea-pig) called 

 forth no such alteration, so that the action is strictly specific to the mouse. 



These effects are best brought out when the inoculations are made with the 

 smallest convenient dose capable of giving rise to maximal percentages of 

 tumours and which lies in our experiments between 1 and 2 centigrammes. 

 "When larger doses (5 centigrammes) are employed, the percentage of tumours 

 developing in the treated animals rose, although it did not reach that in 

 control animals, and the tumours which did develop also remained smaller. 

 In one experiment, however, in which massive doses were inoculated, tumours 

 subsequently developed in the animals in which no growth had appeared 

 within 10 days. Here, apparently, the larger dose of tumour had exhausted 

 the protective property, and subsequently growth was possible. The resist- 

 ance of animals in which spontaneous absorption has occurred has not been 

 overcome in the same way by increasing the dose of tissue inoculated. 

 Whether this points to a difference in degree only, or a qualitative difference 

 in the protection in the two cases, remains to be determined. 



The nature of the action which the body fluids of protected animals have 

 upon tumour tissue in the days immediately following transplantation has 

 been approached in the following manner, after failure to obtain satisfactory 

 results in the test-tube. The failure signifies nothing particular, and may be 

 due either to low degree of protection or imply merely that a complex action 

 takes place in the body, and one we have not reproduced in vitro. 



A number of animals in which tumours had spontaneously disappeared 

 were inoculated with large doses of tumour tissue, and at the same time twice 

 as many normal animals were inoculated in the same way. After varying 

 intervals the implanted tissue was removed from the protected animals and 

 transferred to young normal animals, and the results compared with those 

 obtained by re-inoculating the tissue removed from a similar number of the 

 control animals, sufficient of whom were left alive to prove the vitality of the 

 tissues inoculated in the first instance. These experiments are still in 

 progress, but there seems little doubt that, as compared with normal animals, 

 the tumour tissue rapidly dies in those protected by spontaneous absorption. 



Summary. 



Many apparently contradictory statements as to induced resistance of mice 

 to inoculation may be harmonised when due attention is paid to (1) the 

 susceptibility of young mice and the refractoriness of old mice, (2) to the 

 variations in success which depend on the size of the dose of tumour 

 inoculated, and (3) on the varying qualities of the cells of any one tumour 



