370 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



means of this method, could show that if multiple inoculations of pieces from 

 the same tumor were made into different individuals belonging to such a 

 closely inbred strain, almost all of the inoculated pieces behaved alike in 

 the same individual. Thus there was proved definitely the view the writer 

 had expressed previously (1902), that all transplants from the same donor 

 into the same host should elicit about the same reaction in the latter, the re- 

 actions depending, as we expressed it subsequently, on the relations of the 

 individually differentials of host and transplants. Bittner furthermore found 

 that if a closely inbred strain is used, the growth rhythms, described by Bash- 

 ford as inherent in the character of tumor cells, do not occur. This agreed 

 with the findings of Fleisher, who also had arrived at the conclusion that 

 such rhythms do not exist. 



Little, L. C. Strong, Bittner and Cloudman, noted that if a tumor originates 

 in one of the inbred parent strains, it can be transplanted into all the individ- 

 uals of this strain, but not, as a rule, into the individuals of another inbred 

 strain. These observations are in agreement with the theory of the organismal 

 differentials and accord with the earlier data established in experiments in 

 which less closely inbred strains had been used. If two inbred strains are 

 hybridized, a tumor which had developed in an animal belonging to one of 

 the two parent strains grows well in all or almost all of the F 1 hybrids, while 

 in the F 2 hybrids only a certain percentage of individuals is susceptible to the 

 growth of the transplants in accordance with the rules of Mendelian segrega- 

 tion, and as mentioned above, this percentage figure, according to these in- 

 vestigators, can be used as an indicator of the number of factors which must 

 be present in the hosts if the tumor shall take. The percentage of successful 

 transplantations of the tumor into backcrosses between F 1 hybrids and each of 

 the two parent strains indicates how many of the required growth factors in 

 the hybrids have been contributed by each one of the two parent strains. As 

 should be expected, according to the theory of the organismal differentials, 

 a tumor which originates in an F x hybrid takes readily in all the F 1 hybrids, 

 but not at all or very poorly in the parent strains, and it grows in a certain 

 percentage of mice of the F 2 generation ; this observation is also in agreement 

 with the finding of Tyzzer that a tumor originating in a hybrid F x between 

 Japanese and white mice, could not be transplanted into either of the parent 

 strains. Strong compared the growth of two adenocarcinomata developing in 

 two individuals belonging to the same inbred strain of mice. Because of the 

 close inbreeding of this strain, we should have expected the tissues of the two 

 adenomata to possess approximately the same individuality differentials; 

 but Strong found that these two tumors behaved in a different way after in- 

 oculation into F 2 generations of hybrids between a strain of mice which was 

 susceptible to the tumors and another strain which was non-susceptible. There- 

 fore he concluded that the two tumors, although they had developed in in- 

 dividuals which should be expected to be genetically identical, differed from 

 each other in their genetic constitution, and further, that two tumors struc- 

 turally indistinguishable from each other may differ in their physiological 

 behavior, an observation which in certain respects agrees with our own that 



