TRANSPLANTATION OF TUMORS 395 



transplantability of tumors into different kinds of hosts, such as the growth 

 energy of tumors and their power to adapt themselves to conditions present 

 in the hosts. These characteristics, or the potentiality to develop them, were 

 acquired during the process of the transformation of normal tissue cells into 

 cancer cells, and this transformation is due to the interaction of genetic factors, 

 transmitted by the germ cells, with variable stimulating factors ; both these sets 

 of factors, the intrinsic genetic and the extrinsic stimulating ones, are active 

 in the organism in which the transformation to cancer occurs. Such a process 

 is a graded one, which takes place step by step, and it is probable that to the 

 stage which has been reached in this transformation there correspond different 

 degrees of those characteristics which distinguish tumors from normal tissues. 

 Prominent among these characteristics is the increase in growth momentum 

 and the range of variations which the growth momentum may undergo, and 

 it is probable also that the ability to undergo adaptive changes was acquired, or 

 at least intensified, during the cancerous transformation. 



That adaptive changes to conditions otherwise injurious may be effected in 

 tumor cells has been shown in a more direct way in experiments by Fleisher 

 and the writer. We observed that intravenous injections of solutions of 

 colloidal copper into mice diminish the growth-rapidity of a mammary gland 

 carcinoma in these animals; but if tumors that have been subjected to the 

 influence of colloidal copper for some time, are then transplanted into other 

 mice which subsequently were injected with solutions of this substance, the 

 developing tumors were found to be more resistant to the action of colloidal 

 copper than a line of transplanted carcinomas which had not previously been 

 treated in this way. Similar effects were noted when hirudin was substituted 

 for colloidal copper. Both of these substances immunized the tumor cells in a 

 specific manner. A corresponding decrease in the effectiveness of these tumor 

 growth-inhibiting agencies could be observed if mice bearing adenocarcinoma 

 No. IX were injected with either of these two substances from the second to 

 the sixth day following transplantation, and again from the ninth to the thir- 

 teenth day; the effect of the second series of injections was diminished 

 as the result of the immunizing influence of the early injections. This 

 immunization affected the bearer of the tumor as well as the tumor itself. 

 Likewise, some more recent experiments of Lignac suggest that the cells of a 

 mouse sarcoma may adapt themselves to the action of trypan blue injected into 

 mice ; here, also, it seems that we have to deal with an immunization of tumor 

 cells. Apparently, then, tumor cells may behave in a similar manner to try- 

 panosomes, which also may become adapted to various injurious substances, 

 such as trypanicidal preparations of arsenic. 



We may then conclude that the increase which in many instances takes place 

 in the growth energy and in the number of growing tumors following trans- 

 plantation of spontaneous tumors, is due to different factors which have to be 

 kept distinct. In the first place, the process of transplantation as such produces 

 an augmented growth energy ; this may be due to mechanical stimulations 

 similar to those which induce regenerative growth. In addition there may, 

 under certain conditions, come into play perhaps a direct stimulating effect of 



