TUMORS AND NORMAL TISSUES 357 



spleen and other organs were fully differentiated, the growth ceased and the 

 transplant died. From more recent experiments, it appears that not only the 

 allantoic membrane, but also the yolk-sac of the chick embryo, is suitable for 

 the growth of the heterogenous tumors (Taylor, Thacker and Pennington). 

 Shirai and Murphy noted a better growth of heterogenous tumors in the 

 brain than in the subcutaneous tissue ; the lymphocytic reaction was diminished 

 in these instances if contact with the meninges was avoided. Greene and Saxton 

 succeeded in transplanting into the anterior chamber of the eye of- rabbits, 

 homoiogenous tumors which failed to grow when the usual modes of trans- 

 plantation were tried. In 1937, a Russian investigator, Smirnova, observed 

 that human and mouse tumors grew from four to six months in the anterior 

 chamber of the eye of rats. Greene carried out successful serial transplanta- 

 tions of rabbit tumors in the anterior chamber of the eye of guinea pigs; a 

 human fibrosarcoma, and even a human scirrhous cancer of the mammary 

 gland, grew in this organ. The chick chorio-allantoic membrane, the brain and 

 the anterior chamber of the eye represent places where the aggressive reactions 

 on the part of the host are diminished. In a previous chapter we have dis- 

 cussed already, to some extent, the factors which make possible a better 

 growth of heterogenous embryonal and tumor tissues in these places and we 

 shall return to this problem later, when we' analyze the processes of immunity 

 which develop againts transplanted tumors. In this connection we may refer 

 also to long-continued growth of benign and malignant tumors in roller-tube 

 tissue cultures, in which the medium consisted of coagulated chicken plasma 

 covered by human serum (Gey, Coman). 



Also by other means it was possible to improve the growth of tumors in 

 hosts bearing strange individuality or species differentials. Thus it was found 

 that after previous irradiation of the host by a sufficient dose of X-rays the 

 resistance of the latter against the growth of homoiogenous as well as of 

 heterogenous tumors was diminished (Murphy, Clemmensen and others). 

 Moreover, the transfer of mouse leucosis to otherwise unfavorable hosts 

 could be promoted by these means (Krebs, Furth). Not only tumor and 

 leukemic cells could thus be transferred more successfully, but also Shope's 

 rabbit fibroma virus, when injected into X-rayed or tarred rabbits, caused 

 generalized fibromatosis, the tumors showed a prolonged growth in these 

 animals and in one case the fibroma assumed a sarcomatous character (An- 

 drewes). According to Maisin and Masse, also minced embryonal chick tissue 

 develops, in chickens previously treated with tar, into larger embryomata, 

 which persist for a longer time. Injections of trypan blue and of other 

 colloidal substances (Lignac, Ludford, Andervont) diminish the resistance 

 to the growth of tumors in homoiogenous hosts, and in addition, trypan blue 

 inhibits the development of some types of immunity (Andervont). 



These various agents, X-rays, colloidal dyes and tarring, act presumably on 

 the reticulo-endothelial system, the usual place for the production of general- 

 ized immune reactions. On the other hand, the possibility must be considered 

 that also the primary reactions against strange normal tissue, tumor or virus, 

 due to the presence of preformed substances, may depend upon the reticulo- 



