4 Trans. Acad. Sci. of St. Louis 



It is possible to remove cancer cells which develop in 

 an animal from the original host and transplant them in- 

 to other individuals of the same species. We may re- 

 peat reinoculation indefinitely, carrying the cells from 

 animal to animal. This has been done in mice and rats. 

 A swelling develops, which ordinarily is not painful, but 

 merely weakens the animals. Now such transplanted 

 cells, which grow in an individual, different from that in 

 which they originated, are strange to the new organism, 

 and thus defense processes may be set up and a certain 

 immunity be produced against these grafted cancers, 

 But this is an immunity against body cells of a strange 

 individual and not an immunity against a microorganism, 

 such as we find it in infectious diseases. 



Cancer is then an abnormal growth process. It re- 

 peats in an exaggerated and irregular and endless way 

 what may take place normally in a regular and self -lim- 

 ited manner during the embryonic development or in the 

 repair of wounds in various organs, or after the grafting 

 of tissues to different places. Under all those conditions 

 we find an increased cell multiplication and we may even 

 find an invasive growth. But under normal conditions 

 all this is limited and comes to an end as soon as a certain 

 stage in the process has been reached. It may, however, 

 occur that processes of a typical embryonic development, 

 or wound healing, which is kept up over a long period of 

 time, change into the endless, continuous excess growth 

 of cancer. We shall refer to that again later. 



What are the causes of this excessive multiplication 

 and invasiveness of a limited number of well defined 

 cells of our body which in the end succeed in destroying 

 themselves? As late as ten years ago the majority of 

 physicians would probably have answered this question 

 by stating that the causes of cancer are unknown to us; 

 that the causes of tuberculosis and other infectious dis- 

 eases, on the other hand, have been fully determined. 



