TUMORS AND NORMAL TISSUES 359 



tures, but a part of the tumor itself. The tumors grew, as a rule, only in the 

 same animal in which they originated and not in other animals of the same 

 species. The individuality differential, therefore, asserted itself under these 

 conditions. This was observed in some of our experiments, as well as in those 

 of Ribbert and Mann, but we, as well as subsequent investigators, found that 

 different benign tumors may differ in their power of resistance to homoio- 

 toxins, it being possible to transplant certain of them serially into other in- 

 dividuals of the same species. We observed, furthermore, that while after 

 transplantation of carcinoma or sarcoma, the greater part of the transplant 

 became necrotic and only a small peripheral zone remained alive, in the case 

 of these benign tumors of the mammary gland a greater portion of the pe- 

 ripheral tissue could be preserved, and in some autotransplanted tumors even 

 almost the whole of the transplant; evidently some of the constituent parts of 

 the tumors, especially the fibrous ones, were more resistant than very cellu- 

 lar and rapidly dividing malignant cells. In addition, while with malignant 

 tumors as a rule, an increase in growth energy occurred in the course of the 

 first few transplantations, such an increase was lacking with these adenofibro- 

 mata. In our experiments there was a gradual decline in the growth energy 

 after successive transplantations. Another difference between these two types 

 of tumors consisted in the different effects which hormones exerted on their 

 growth. Cancerous tissues, in particular carcinomas of the mammary gland, 

 are no longer accessible to the action of ovarian hormones, whereas a positive 

 effect was quite evident in the case of benign tumors of the mammary gland ; 

 such tumors retained the ability to respond with marked growth processes to 

 the action of hormones, which determine the growth processes in the normal 

 breast tissue during pregnancy. The cells of these adenofibromata evidently 

 had not changed their physiological characteristics to the same extent as the 

 cells of malignant mammary gland tumors. Moreover, while in our experi- 

 ments the tumors were propagated mainly in female rats they were able, also 

 to grow in male rats. 



It may therefore be concluded that the fate of the transplanted benign 

 tumor depends not only on the organismal differentials, but also on its mode 

 of growth and some other factors, which are localized either in the tumor 

 cells themselves or are circulating in the bodyfluids of the host. Some of the 

 factors localized in the tumor cells correspond to those present also in normal 

 tissues, in particular, the organ or tissue differentials, which help to determine 

 whether a tissue is able to withstand the injury connected with autotrans- 

 plantation. 



A further factor in determining transplantability is the increase in growth 

 energy acquired by normal tissues during their transformation into benign 

 tumors. This additionl growth is relatively slight, although it varies in different 

 benign tumors. Correspondingly, the morphological and biochemical modi- 

 fications, which the normal tissues undergo during their change into benign 

 tumors, are less marked than those which take place during their change into 

 malignant tumors. In this respect again, different benign tumors may behave 

 somewhat differently, and it should therefore be expected that they show a 



