410 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



less pronounced than that following a spontaneous retrogression of a larger 

 tumor which at first grew well. Lumsden similarly observed that the im- 

 munity is greater after retrogression of large than of small tumors. It may 

 be assumed that in order to accomplish the retrogression of an actively grow- 

 ing large tumor, a higher degree of immunity will be required than for the 

 retrogression of a weak tumor, and more immune substances will therefore 

 subsequently be available for combating the growth of a second tumor. As 

 stated, this high degree of immunity necessary for the absorption of large 

 tumors is achieved only if the individuality differentials of host and trans- 

 plant are sufficiently different to cause a primary incompatibility, which 

 must, however, not be so great that it prevents growth of a tumor during the 

 early periods following transplantation. Subsequently, it must be assumed, 

 the quantity of immune substances increases at a rate too rapid for the 

 neutralizing power of the tumor. However, we have seen that also the im- 

 munity induced by a growing tumor is greater if the first tumor grows 

 vigorously, than if it has been weakened in its growth intensity. 



That immune substances are produced under these circumstances and may 

 be present in the spleen of the tumor-bearing animals is indicated by the 

 experiments of Mottram and Russ, as well as of Woglom, who show that 

 in the spleen of animals in which tumors had retrogressed, substances are 

 present which injure the cells of a similar tumor. As mentioned previously, 

 Woglom's recent investigations suggest the possibility that the antibodies 

 circulating in the bodyfluids of an immune animal can be absorbed by 

 tumor mash. These substances, then, are able to injure in vitro a piece of 

 tumor and prevent its successful transplantation ; and likewise Lumsden has 

 found that substances circulating in the blood of rats, rendered immune against 

 rat sarcoma, succeeded in killing cancer cells as well as spleen cells of the 

 same species growing in vitro. As stated in a preceding chapter, Lumsden 

 attributes these effects to "antimalignancy" immune bodies, devoted as 

 a result of the growth of a homoiogenous sarcoma ; but Phelps and others 

 interpret them as due to cytotoxins, which form in response to the presence 

 of strange species or individuality differentials, since these reactions occur 

 also with normal spleen cells and may be elicited by antigens present in normal 

 spleen. 



In addition to cytotoxins, there may be found in the bearers of retrogressed 

 tumors hemagglutinins, which may, however, affect not only erythrocytes, 

 but also other kinds of cells (Gorer, Lumsden). Lumsden has made it probable 

 that these cytotoxins and hemagglutinins are distinct and develop independ- 

 ently of each other; he also observed a definite relation between the strength 

 of such antibodies and the retrogressive changes which take place in the 

 tumor; this would indicate that retrogression is due to the action of immune 

 substances. However, while it is quite probable that the latter aid in the 

 injury of the tumor, it is probable also that primary mechanisms are involved, 

 and that the immune substances originate as a reaction against primary 

 incompatibilities between organismal differentials. 



Lumsden noted that the erythrocytes of a rat may possess an agglutinogen, 



