IMMUNITY IN TUMOR TRANSPLANTATION 407 



differentials which have been given off by the tumor into the circulation and 

 which act as antigens. Also, Seelig and Fleisher observed such a balancing 

 between the growth energy of the first and second tumors and they noted that 

 the tumor with the greater growth energy has the advantage over a weaker 

 tumor. In addition, they found that intraperitoneal inoculation with tumor ma- 

 terial may exert a greater immunizing power than a subcutaneous inoculation, 

 although the intraperitoneal inoculation may not be followed by actual growth 

 of the carcinomatous tissue. In this case we may have to deal with an immunity 

 similar to that which is caused by inoculation of normal or tumor tissues which 

 do not noticeably grow. 



This method of using an originally active, virulent tumor, after its growth 

 energy has been experimentally reduced, for the demonstration of immune 

 processes which otherwise would not be manifest, was subsequently employed 

 also by Tsurumi, as well as by Rohdenburg and Bullock, and in a modified 

 way by Caspari and his collaborators, Schwarz and Ascoli. Besides grading 

 the growth energy by means of heat, they accomplished the same purpose also 

 by exposing the tumors to the action of radiation or of various chemicals. Only 

 when the inoculated tumor material was living did they find an immunizing 

 effect. Presumably the injured tumor grew temporarily to a slight extent, but 

 it soon retrogressed, and it is possible that the immunization was accomplished 

 by living but not growing material. However, the essential point is that a 

 balancing may take place between the first and second tumor pieces in ac- 

 cordance with the degree of potential growth energy which each inoculated 

 piece possesses; and Caspari and Ascoli also observed such an effect. The 

 greater the growth energy of the first piece, the more it tends to diminish the 

 growth energy of the tumor developing from the second piece ; furthermore, 

 the influence of the first piece is inversely proportional to the growth energy 

 of the second. In a similar manner Lumsden has recently demonstrated that 

 by weakening the growth of a second transplanted piece of cancerous tissue 

 in various other ways, such as by inoculation in unfavorable places, constric- 

 tion of the blood vessels leading to the tumor, by means of ligatures, and in- 

 jection of formalin into the transplant, it is possible to prove that tumors like 

 the Twort mouse carcinoma or mouse carcinoma 63, which, according to Rus- 

 sell, belong to the type of tumors which do not elicit concomitant immunity, 

 may give rise to such an immunity. Of interest is the observation of Foulds that 

 parallel to changes in their growth energy, tumors in the course of continued 

 transplantations may undergo variations in their power to elicit concomitant 

 immunity. The effects which a first growing tumor exerts on a second one 

 may further depend also on the kind of tumors used. For instance, the growth 

 of a secondarily transplanted mouse chondroma, a very slow-growing tumor, 

 was apparently not affected by a first tumor of the same kind, because these 

 cartilage tumors are very resistant to injurious influences. 



We may therefore conclude that even tumors whose growth apparently 

 does not lead to the development of immune processes, may actually have this 

 effect provided their individuality differential differs from that of the host. 

 The existence of concomitant immunity may then, in general, be ascribed to 



