430 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



have shown that spontaneous as well as long-transplanted tumors, and also 

 rapidly growing embryonal tissues, contain antigens which are also present 

 in dying leucocytes (pus) and in necrotic tissue. Antigens which are common 

 to long-transplanted tumors and pus are species-specific; for instance, the 

 Brown-Pearce rabbit carcinoma has an antigen in common with rabbit pus, 

 and the guinea pig liposarcoma has an antigen in common with guinea pig pus. 



We have already mentioned the fact that in the sera of animals which bear 

 virus-induced cancers antibodies may be demonstrable, which are directed 

 against the virus. Such sera may contain substances which neutralize the virus, 

 or in combining with a virus antigen, call forth complement fixation or lead to 

 the formation of precipitates. Thus the filtrable Rous fowl sarcoma contains 

 virus antigen which may induce in the blood of geese, injected with the tumor 

 extract, antibodies against this virus (Rous, Robertson and Oliver). Similar 

 immune substances may be demonstrated in the serum of chickens in which 

 such tumors have retrogressed (Rous, Mottram). They may also develop in 

 bearers of slowly growing tumors of this kind (Andrewes) and one kind of 

 tumor may elicit the production of antibodies which interact also with the 

 virus of a different type of fowl sarcoma. According to Peyton Rous and 

 Kidd, the growth of the rabbit papilloma, which is caused by a virus, as well 

 as carcinoma which develops from this papilloma, may give rise to specific 

 immune substances circulating in the serum of the bearer of this newformation. 

 In saline extracts of the cottontail rabbit papillomas, a serologically specific 

 substance can be demonstrated, which probably is identical with the Shope 

 papilloma virus. It is of special importance that, according to Rous, if a 

 papilloma virus-induced carcinoma develops in domestic rabbits, the virus is 

 no longer demonstrable in the tumor extracts; but the presence of such a 

 virus can be made very probable, because specific antibodies against the 

 papilloma virus are demonstrable in the blood serum of these rabbits. Similarly, 

 Andrewes has shown that when sarcoma is produced in fowl by injection of 

 carcinogenic substances and a filtrable agent cannot be shown to exist in this 

 tumor by direct methods, the presence of a hidden agent in the tumor may be 

 made probable by means of immune substances which can be shown to exist 

 in the blood serum of the fowl. Kidd found, with the aid of the complement 

 fixation method, an antigen in the extract of the Brown-Pearce rabbit car- 

 cinoma ; this antigen was not of the same type as the antigens present in 

 normal rabbit organs, nor was such an antigen noted in tumors occurring in 

 the uterus of the rabbit ; but this antigen was also distinct from the rabbit 

 papilloma antigen and the presence of a virus has not so far been demonstrated 

 in the Brown-Pearce rabbit carcinoma. 



In this connection it may also be of interest to recall the experiments of 

 Furth on transplantation of leukemic cells from a case of leukosis which arose 

 in F x hybrids between two strains of mice differing markedly in their tendency 

 to become leukemic. The results of transplantations from F t hybrids to both 

 parent strains could not be interpreted merely as due to differences in the 

 relationships of the individuality differentials of the two parent strains and 

 the hybrids. We suggested that exogenous growth stimuli (Ge), acting spe- 



