420 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



resistance and susceptibility to tumor growth can be gauged by their effects 

 on the lymphocytes. In accordance with the views expressed by Da Fano, 

 Murphy believes that the lymphocytic reaction which develops around a tumor 

 graft in an immunized animal is the local manifestation of a general reaction 

 which takes place in the animal. When mice are naturally immune against a 

 tumor graft, or when they have been made immune by experimental means, 

 they show an immediate and very marked increase in the number of circulat- 

 ing lymphocytes following inoculation with a piece of tumor against which 

 they are immune, whereas, the other blood cells show no change. Similarly, in 

 the lymph glands of a mouse which has been immunized experimentally, or in 

 which immune processes set in following absorption of its tumor, the mitotic 

 proliferation of the lymphocytes is much increased, and it is still further in- 

 creased after a second inoculation of a tumor piece. From all these observa- 

 tions Murphy concluded that the general, as well as the localized lymphocytic 

 reaction is not merely a condition accompanying tumor immunity, but that it 

 is responsible for the development of this immunity, and as stated above, he 

 found that even an otherwise successful autogenous transplantation of spon- 

 taneous tumors can be prevented through an increase in the activity of 

 lymphocytes. 



There were various other experiments which seemed to support this inter- 

 pretation. Thus Murphy found that if pieces of heterogenous (mammalian) 

 tumors or embryonal tissues were transplanted on the chick allantoic mem- 

 brane, they grew for some time. However, if he transplanted simultaneously 

 with the mammalian tumor small pieces of chicken spleen or bone marrow, 

 the tumor did not grow, presumably because of the injurious action of the 

 lymphocytes contained in the latter organs. Accordingly, growth of the tumor 

 ceased at the time when, in the eighteen or twenty-day-old chick embryo, the 

 spleen begins normally to function. But, Danchakoff maintains that it is not 

 the lymphocytes of the transplanted spleen or bone marrow which grow out 

 towards the tumor and injure it, but monocytes or reticuloendothelial cells. 



There are other regions in the body where the resistance offered to the 

 growth of homoiogenous or heterogenous tumors is distinctly lessened. Ref- 

 rence has been made to the diminution in the intensity of the lymphocytic 

 reaction after homoiotransplantation of normal tissues into the brain. Ebeling 

 ( 1914) had found indications that in mice which are immune to subcutaneous 

 inoculation of mouse carcinoma, transplantation into the brain might still be 

 successful. According to the subsequent observation of Shirai, it was possible 

 to transplant mammalian tumors into the brain of a strange species. Murphy 

 likewise noted that heterotransplantation of tumors into the brain may be 

 more successful than transplantation into other parts of the mammalian or- 

 ganisms, and moreover, that the lymphocytic reaction is lacking here pro- 

 vided the transplant has not been in contact with the meninges or with the 

 choroid plexus. Active immunization which was sufficient to prevent tumor 

 growth subcutaneously, was ineffective against a tumor grafted into the brain ; 

 but again, a simultaneous transplantation of a piece of spleen tissue into the 

 brain caused the mechanisms of defense against the heterogenous tumor to 



