TUMORS AND NORMAL TISSUES 345 



the host possessing in all probability the same or almost the same individuality 

 differential. 



The most probable interpretation of this experiment seems to be that the 

 growth of the first homoiogenous tumor causes the production of an im- 

 mune substance, injurious to the growth of this tumor. However, this in- 

 jurious substance is, to a large extent, absorbed and neutralized by the growing 

 homoiogenous tumor itself. If now this tumor is extirpated, the immune sub- 

 stance is no longer neutralized and it is thus able to prevent the growth of a 

 second homoiogenous tumor. Besides, this immune body must carry a differen- 

 tial able to combine with the homoiogenous differential of the transplanted tu- 

 mors, while the tissues of the host animal, as well as those composing the 

 autogenous tumor, being the bearers of an autogenous differential, are not able 

 to remove and to neutralize this substance. Substances which carry a homoiog- 

 enous individuality differential may then induce in the host immune re- 

 actions antagonistic to the growth of homoiogenous tumors, but they are 

 not absorbed and neutralized by autogenous tissues. It would be of interest 

 to determine whether the immunity procured in the Uhlenhuth phenomenon 

 is a specific one, directed only against a certain homoiogenous tumor, or 

 whether it also protects against other types which carry different homoiog- 

 enous individuality differentials. In accordance with this interpretation 

 it may then be concluded that antibodies are produced by growing homoiog- 

 enous, but not by autogenous tumors, and furthermore, that such antibodies 

 are neutralized by homoiogenous but not by autogenous tissues ; but at any 

 given time, the amount of such antibodies circulating in the bodyfluids may be 

 too small for direct demonstration by the ordinary serological methods. 



There is another set of experimental data which confirms and further 

 extends these conclusions as to the importance to be attached to the difference 

 between autogenous and homoiogenous differentials. It has been found possible 

 (Schoene, Bashford) to immunize mice, although only to a limited extent, 

 against the growth of a homoiogenous, transplantable mammary carcinoma 

 by a previous inoculation of normal tissues, such as erythrocytes, embry- 

 onal material, liver and spleen. As a matter of routine, the tissue used for 

 immunization was taken from other animals of the same species. Woglom 

 however, tested the immunizing power of a piece of the animal's own spleen. 

 At first he believed that the inoculations of such autogenous tissue also pro- 

 duced a positive result, but the subsequent experiments of Apolant and 

 Marks, as well as of Woglom himself, showed that neither the animal's 

 own spleen tissue nor its erythrocytes had any demonstrable immunizing 

 action, while inoculation of the tissue of other animals of the same species 

 was effective. We may then state that a difference in individuality differen- 

 tials is a prerequisite for the production of immunity, that it is presumably 

 the strange differential itself which is concerned in this process of immuni- 

 zation, and that identity of organismal differentials, in the immunizing ma- 

 terial and in the animal which is to be immunized, precludes an effective 

 immunization ; this observation is in harmony with the fact that a transplant 



