TRANSPLANTATION OF TUMORS 387 



If, following exposure to a sufficiently intense heat the tumor cells are 

 injured, they may no longer be able to resist to the same degree as normal 

 cancer, the activity of the connective tissue of the host, which thus begins 

 to envelope the tumor with a fibrous capsule and to restrict its expansive 

 growth. But following transplantation into a new host, a recovery of the 

 tumor again may be accomplished and the tumor cells may now predominate 

 over the stroma cells of the host. Furthermore, in accordance with the 

 diminution in growth energy following the heating, we found that the 

 number of cells undergoing mitotic division is distinctly diminished, although 

 mitoses are not quite suspended ; however, mitotic proliferation may occur, 

 as we have shown formerly, even in retrogressing tumors. Lastly, we noted 

 that as the result of the depression in growth energy following heating, cer- 

 tain reparative processes, which otherwise could take place in the tumor, are 

 inhibited ; thus the growth of active tumor cells into the central necrotic areas 

 and the replacement of the latter by these cells are retarded. As these experi- 

 ments show, we are able to produce through experimental interference, 

 depressions in the growth energy of tumors, with or without subsequent 

 complete recovery, or with only a temporary recovery. A similar diminution 

 in growth energy, number of mitoses and, oxygen intake, has been observed 

 by Maus, Craig and Salter after transplantation of mouse sarcoma 180 into 

 immunized mice; as a result of the immune processes, conditions injurious 

 for the tumor cells had been created. 



The experiments to which we have referred so far, concern sarcoma, but 

 similar results can be obtained also in experiments with carcinoma. Thus, 

 the writer and E. P. Corson-White observed that if the growth energy has 

 been depressed, either through graded heating of the pieces of carcinoma 

 preceding transplantation or through transplantation of the tumor into 

 unfavorable strains of mice bearing a different strain differential, transplanta- 

 tion of the injured tumor cells into other more favorable mice might lead 

 to the development of tumors which grew much more actively than the 

 injured tumor which had been used for transplantation, although as a 

 general rule the tumors developing under these conditions showed less 

 growth energy than the average normal carcinoma No. IX. It was possible 

 through continued serial transplantation of depressed tumors to raise still 

 further their growth energy. In this manner, tumor tissue which otherwise 

 would have perished, could be saved. But also in this series, as in the 

 preceding one, grafted pieces of tumor failed to develop when once a certain 

 stage of retrogression had been reached. Certain types of tumors which are 

 presumably very sensitive to injury may therefore not respond to these 

 procedures with a resumption of their growth energy. It seems, moreover, 

 that in different types of tumors the inherent potential growth energy differs 

 and the behavior of retrogressing or stationary tumors may depend also 

 upon this factor. There is a constant balancing between the inherent growth 

 energy and antagonistic factors, such as marked differences between the 

 organismal differentials of host and transplant, or direct injury of the tumor 

 caused by the graded application of heat or of certain chemicals, or, in some 



