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



(atreptic immunity) : the tumour already established withdraws special 

 nutritive substances (substance X) from the circulation, so that the new 

 graft cannot grow. A similar explanation is invoked for the rarity, or small 

 size, of metastasis in mice with large transplanted growths. Eepeated 

 inoculation of negative mice leads to a very refractory condition in the 

 animals which never develop tumours. 



Eats can be successfully inoculated with rapidly growing mouse tumours. 

 Growth proceeds for a time and then ceases (atrepsie), and the animals are 

 then refractory to further inoculation (active immunity). 



Summary of the Present Investigation. 

 After discussing : — 



1. The distinction to be drawn between the conditions of origin of a 

 sporadic tumour and the conditions of growth of cancer in mice, and its 

 bearing on experimental investigations. 



2. The importance of natural variations in the resistance of mice to 

 inoculation and of inherent variations in the energy of growth of the 

 tumour cells. 



We shall adduce evidence that : — 



3. Mice in which a growing carcinoma has been spontaneously absorbed 

 may be completely protected against subsequent inoculation of the same 

 growth, and to a lesser extent against other and different growths. 

 Similarly, protection follows absorption of tumours after exposure to radium. 



4. Protection may be induced, or, when naturally present, enhanced by 

 the inoculation of tumour material when no growth has resulted. This 

 protection is specific, and has only been induced in mice by the inoculation 

 of mouse tumours, and not by those of strange species. This specificity has 

 an important bearing on the nature of cancer. 



5. Protection can also be induced by the inoculation of normal mouse 

 tissues, and particularly by the inoculation of blood. 



"We shall discuss the probable nature of the protection conferred ; its action 

 by means of the body fluids, at any rate in part, leading to the death of the 

 cancer cells after short sojourn in the body of protected animals. 



(1) The Distinction to be drawn between the Conditions of Origin 

 of a Sporadic Tumour and the Conditions of Growth of Cancer 

 in Mice, and its bearing on Experimental Investigations. 



When the energy of growth of the cells of a propagable tumour is great 

 and a high percentage of all inoculations are successful, the variations in the 



