IMMUNITY IN TUMOR TRANSPLANTATION 411 



which is present also in rat sarcoma cells, as demonstrated by the agglutina- 

 tion of these rat red corpuscles when mixed with the serum of a rat made 

 immune against a rat sarcoma. If pieces of rat sarcoma are transplanted 

 into such a rat, immune substances would not be produced, because of the 

 presence of a common antigen in the sarcoma cells and in the host cells, and 

 hence an inoculated piece of rat sarcoma would grow. In this case an agglu- 

 tinogen present would, therefore, make possible the growth of a transplanted 

 tumor and would actually function as a susceptibility factor for this tumor. 

 We have discussed these observations already in a preceding chapter. 



The histological changes which are observed around retrogressing tumors 

 do not explain the character of the immunity noted in these animals. Thus 

 Gaylord and Clowes, and others, found necrosis and hemorrhages, as well 

 as collections of lymphocytes in or around such retrogressing tumors ; the 

 presence of lymphocytes may be taken to indicate an active reaction on the 

 part of the host against the transplant. However, Ishii and the writer, in 

 examining tumors that retrogressed following an in vitro exposure to heat, 

 did not observe such collections of lymphocytes ; there was merely a connec- 

 tive tissue capsule around the tumor and a replacement of parts of the tumor 

 by fibrous tissue. 



It is an interesting problem as to whether the immunity thus produced is 

 specific for the tumor which has retrogressed, or whether it applies also to 

 other types of tumors. Bashford assumed it to be specific, because he noticed 

 that mice in which an immunity had developed after retrogression of a car- 

 cinoma were immune against a re-inoculated carcinoma, but not against a 

 sarcoma. However, as Caspari and others have pointed out, this result is 

 probably to be explained by the difference between the growth energy of the 

 mouse sarcoma and that of the carcinoma ; an immunity sufficient to prevent 

 the growth of a carcinoma, may not have been sufficient to prevent that of a 

 much more active sarcoma. In general, the specific immunity which has been 

 acquired is directed against strange individuality differentials in case of 

 retrogression of a homoiogenous tumor, and against a particular species 

 differential after retrogression of a heterogenous tumor. The "retrogression" 

 immunity is therefore essentially an immunity directed against organismal 

 differentials which are common to various kinds of tissues and tumors belong- 

 ing to the same species ; it represents what Ehrlich called "pan-immunity," 

 by which he meant an immunity directed not only against a tumor composed 

 of a certain kind of tissue, but also against a tumor composed of another kind 

 of tissue of the same species. Nevertheless, the immunity may be greater 

 to tumors composed of the same kind of tissues than to another kind of tumor 

 belonging to the same species ; such a partial specificity was observed by 

 Greene after a primary transplantation of homoiogenous tumors of the rabbit 

 into the anterior chamber of the eye, and a second transplantation of the same 

 or of another kind of tumor into the other eye or into the testicle. Under 

 these conditions a growing first tumor seems to act similarly to a retrogressed 

 tumor. In addition to the "pan-immunity" directed against all the individuality 

 differentials of a species, there may exist, therefore, an immunity directed 



