TUMORS AND NORMAL TISSUES 343 



of certain tissues. We concluded further that when the intrinsic factor, 

 which represents the essential stimulus to tumor growth, is very strong, 

 then the substances which determine to what extent tumor cells are able to 

 live in other individuals — the individuality differentials — may become less 

 important in determining the fate of the transplanted tumor. However, there 

 is a limit as to the differences between the individuality differentials of host 

 and transplant if the intrinsic growth stimuli shall be able to assert them- 

 selves. This would represent a special instance of the more general rule that 

 the action of efficient growth stimuli, or expressed differently, a strong 

 growth momentum, may make it possible for tissues to overcome conditions 

 which are unfavorable, not only to the growth but also to the life of these 

 tissues. 



Subsequent experiments of others have confirmed these observations and 

 conclusions. Thus Borrel and Petit, Ribbert and Mann, obtained similar 

 results in horse, dog and cat, respectively, and Tyzzer, Apolant and Haaland 

 found the same differences between auto- and homoiotransplantation in 

 mammary carcinoma of the mouse. While only a relatively small number of 

 spontaneous mouse carcinomata can be readily homoiotransplanted, auto- 

 transplantation almost always succeeds. In accordance with these concep- 

 tions also, were the subsequent findings of Haaland (1910) that inoculation 

 of a transplantable tumor in a mouse did not prevent the later development 

 of a spontaneous tumor in this animal ; nor did the growth of the trans- 

 plantable tumor affect metastasis formation or a subsequent autotransplan- 

 tation of a spontaneous autogenous tumor. Conversely, Haaland observed 

 that the presence of a spontaneous tumor did not noticeably influence the 

 take or the secondary retrogression of a transplantable tumor. Bashford 

 interpreted these differences between the behavior of the transplantable 

 tumors and of spontaneous tumors as an indication that the conditions of 

 transplantation differ from those which determine the origin of a spon- 

 taneous tumor; he did not attribute them to differences in the individuality 

 differentials of host and transplant. While it is true that the conditions deter- 

 mining the first origin of a tumor and its transplantability are different, the 

 essential factor is that a spontaneous tumor represents an autogenous tissue, 

 possessing essentially the same individuality differential as the other tissues 

 of the indvidual in which the tumor originated, whereas the tumor trans- 

 planted into another individual of the same species represents a homoiog- 

 enous tissue with an individuality differential which differs to a greater 

 or lesser degree from that of the host. 



While the growth of a homoiotransplanted tumor does not need to affect 

 the autotransplantation of a spontaneous tumor, there are some observations 

 which indicate that a spontaneous (autogenous) tumor may, under certain 

 conditions, influence the growth of a homoiotransplanted tumor. Thus it 

 seems that spontaneous mouse tumors, which, as we have seen, in the ma- 

 jority of cases are very difficult to transplant into other individuals, can 

 apparently be more readily homoiotransplanted when the host is also the 

 bearer of a spontaneous tumor (Loeb, 1907; and Loeb and Fleisher, 1913 



