CHAPTER XVI. 



IMMUNITY AND SERUM REACTIONS IN REFERENCE TO MALIGNANT TUMORS. 



EXPERIMENTAL TRANSPLANTATION OF TUMORS. IMMUNITY TOWARD TUMORS. 

 SERUM REACTIONS. MEIOSTAGMINE REACTION. 



The etiology of malignant tumors is still unsolved. It has been defi- 

 nitely proven, however, that tumors or at least some of them can be trans- 

 planted. Naturally such experiments with human cancer are still limited 

 and inconclusive, as attempts to transplant growths from one person to 

 another are entirely out of question. On the other hand, the inoculation of 

 human cancer into lower animals has been successful in the hands of only 

 few reliable workers as Dagonet and C. Lewin. 



These failures are the less surprising when one considers that malignant 

 tumors obtained from the lower animals, as rats, and transplanted into 

 other animals of the same species, not infrequently cease to grow in their 

 new surroundings. Successful implantations of spontaneous animal 

 rumors vary very greatly, from 4.1 per cent. (Bashford) to 40 to 50 per 

 cent. (Jensen). The percentage becomes still lower or even entirely 

 negative if the transplantation is made upon animals not of the same 

 but of very closely related species, for example, when the gray house 

 mouse is employed instead of the white mouse. 



Once, however, the tumor continues to proliferate in its new host, it 

 becomes more easily transplan table. Ehrlich has shown that the virulence 

 of a tumor increases the more frequently it is successfully transplanted. 

 Thus a growth can be obtained which may give 90 to 100 per cent, of posi- 

 tive grafts. During this long- continued process, the histological structure 

 of the tumor may change. Not only may a carcinoma be transformed into 

 an adenoma, but even into a sarcoma, as was first observed by Ehrlich and 

 Apolant, and later on by others (Liepmann, Bashford, C. Lewin). 



That an immunity toward carcinoma may possibly exist has been 

 considered. 



This has been based upon the facts that some animals resist all attempts 

 at transplantation (" natural immunity"), that in others the tumor grows 

 only to a limited degree, and that in a few, comparatively large tumors re- 

 cede and disappear spontaneously (" acquired immunity ") . The last class 

 nowremains refractory to all tumors, even the most virulent, thus proving a 

 non-specific immunity ("pan immunity"). Ehrlich attempted to produce 

 an immunity against a highly virulent mouse carcinoma by using as vaccine 

 the hemorrhagic mouse tumor which only rarely allows of transplantation. 



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