i9o8,l LOEB— lUMOR GROWTH AND TISSUE GROWTH. 7 



Here they live, and even grow ; while in other animals of the same 

 species, they die very soon after transplantation. This probably 

 applies to most of human tumors. The same holds good of certain 

 animal tissues and organs ; as, for instance, the ovary. They can 

 much more easily be transplanted into the animal of which they 

 have formed an integral part, than into other animals of the same 

 species. 



There exists another point of similarity between the transplanta- 

 tion of normal tissues and organs, on the one hand, and of tumors, 

 on the other: in both cases, after transplantation, only the peripheral 

 parts of the transplanted piece usually remain alive ; the central part, 

 which is not well supplied with lymph or blood from the host, soon 

 dying. This similarity between the behavior of normal tissues and 

 of tumors after transplantation can be easily explained, if we con- 

 sider that in both cases we have equally to deal with the inoculation 

 of cells or tissues from an animal organism ; and that the trans- 

 planted tumor, as can be readily shown by microscopic examination, 

 grows merely from the transferred tumor-cells themselves, and not 

 from the tissues of the receiving host-animal. 



On the other hand, however, there exist also some very interest- 

 ing differences between the growth of normal tissues and of tumor- 

 tissues after transplantation, the former always growing only very 

 slowly for a time, and then ceasing to grow, or merely remaining 

 alive after transplantation ; and the latter continuing to grow rap- 

 idly, and sometimes continuing to infiltrate the surrounding host- 

 tissue and to make metastases. Their character is not markedly 

 modified through transplantation. Eight years ago I transplanted 

 a sarcoma of a white rat into more than forty generations, without 

 an appreciable decrease in the energy of growth of the tumor cells. The 

 fact that it is possible to propagate tissues of the animal body through 

 years and years in other animals of the same species, without any loss 

 of vitality and power of propagation of the tumor-cells, while they 

 would long since have died if they had remained in the animal to which 

 they originally belonged — suggests, it seems to me, a consideration 

 of great biological significance, namely, the question whether our 

 own body-cells are all equally mortal, or whether their death does 

 depend upon their accidental connection with other cells and with 



