238 C. p. RHOADS 



a dedifferentiated one. Proof of this requires evidence, not now avail- 

 able, that normal differentiated cells are immunologically much more 

 complex than the primitive cell, and both more so than the neoplastic 

 cell. 



The studies of Kidd (11), which are referred to later in detail, are 

 important in their bearing on the question of host resistance to trans- 

 planted tumors. They contain an admirable review of the literature on 

 the subject. Attention is called to the fact that some mechanism of pro- 

 tection against transplants exists other than the one characterized by 

 the presence of humoral antibodies. Kidd shows that whereas comple- 

 ment-fixing substances are frequently associated with regression of 

 the Brown-Pearce tumor, and injure the cells of that tissue, similarly 

 specific antibodies have no effect on the course of the V2 carcinoma. 

 Furthermore, examples are presented of solid immunity in the apparent 

 total absence of such antisera. Barrett (82) has published from Mur- 

 phy's laboratory beautiful experiments which prove the difficulty, if 

 not impossibility, of creating an immune state to cells homozygous 

 with the host. 



In this respect an immunologic study of the differences between the 

 wild strain of Neurospora and the mutant derivatives would be of very 

 great interest. It is not impossible that the more biochemically com- 

 petent wild organism possesses fewer points of immunologic specificity 

 since there is less tendency to accumulate the products of incomplete or 

 abnormal metabolic processes. Were this concept, as presented by Led- 

 erberg (83), to be supported by experimental evidence, the cancer cell 

 could be considered as analogous to the wild strain Neurospora, a back 

 mutation to a completely competent form. It would then become neces- 

 sary to view the normal cell as the mutant, and again differentiation 

 would be seen as the result of a progressive series of mutations with 

 loss of function and thereby the discovery of special functions. 



Abnormal Growth due to Hybridization 



An important experiment in the induction of neoplasms is the work 

 on hybridization. Gordon (84) studied species of two genera of tropical 

 fish and found that hybrids between them resulted in the production of 

 melanotic neoplasms in greater numbers than would occur in the parent 

 species. Whitaker (85) described tumors which occurred in the Fi hy- 

 brids of crosses of Nicotiana glauca and Nicotiana Langsdorfi. He 

 ascribed this result to the introduction of chromosomes of the latter 



