REACTIONS AGAINST INDIVIDUALITY DIFFERENTIALS 69 



tions likewise, as a rule, were constant in pieces of tissue from the same 

 donor, transplanted into the same host, provided we consider that there are 

 various variable factors which complicate such experiments and, in particular, 

 that as a rule only in transplants in which there is a large amount of living 

 tissue left is the lymphocytic infiltration considerable. 



However, there were strong indications that, in addition, another factor 

 played a role in certain instances. Thus we observed that in the same host the 

 reactions against various tissues from two different homoiogenous donors, 

 while not necessarily identical, were correlated with each other. Furthermore, 

 if tissues from two donors were each transplanted into two different hosts, 

 the reactions against both could be severe in one host and relatively mild in 

 the other host. It was especially the Bu rats which, in almost all cases, reacted 

 very severely against transplants from other families or strains of rats, the 

 grade being 1 in the large majority of cases, while the reciprocal transplan- 

 tations, in which Bu rats were the donors and other families the hosts, gave a 

 much greater number of milder reactions. The Bu rats, before being used for 

 transplantation, had been fed for some time on a riboflavin-deficient diet ; but 

 that this was not the essential cause of the strong reaction against strange 

 individuality differentials which these rats exhibited was shown in control 

 experiments, in which this same strain of rats had always been kept on a 

 normal diet, but the severity of the reaction was not diminished ; nor was the 

 age (weight) of the animals used, nor the season of the year when the experi- 

 ments were carried out of significance in this respect. Only in a single experi- 

 ment in which these rats served as hosts were the reactions somewhat milder. 

 While thus the Bu rats reacted in almost all instances very strongly against 

 homoiogenous differentials, the homoiogenous differentials of Wistar rats, 

 serving as donors, seemed to elicit less strong reactions on the part of the host 

 than did some of the other strains, although they still remained within the 

 homoiogenous range. There is, then, some strong experimental evidence for 

 the conclusion that certain strains of rats, and probably also other species, 

 have the peculiarity of reacting especially strongly against strange individuality 

 differentials, and it is furthermore possible that the grafted tissues from cer- 

 tain strains of rats, acting as donors, stimulate the host cells less actively than 

 do the tissues from other strains. A second set of factors exists therefore 

 besides the degree of strangeness between the individuality differentials of 

 host and transplant, which determines the severity of the reaction of the host 

 against the transplant, namely, a peculiar reactivity of the host tissues which 

 presumably has also a genetic basis. There is, besides, some evidence that not 

 only strains of animals have this peculiarity in their mode of reaction, but that 

 also various individuals may differ from one another in this respect. 



4. The effect of heat on the homoiogenous individuality differentials in 

 rats. In these experiments we subjected thyroid and cartilage- fat tissue of 

 Bu rats to boiling temperatures for 5 minutes and then transplanted the pieces 

 into Chicago rats. Under these conditions the homoiotransplanted tissues 

 were entirely necrotic. After 12 days, the nuclei in the thyroid and parathyroid 

 were found dissolved in the peripheral, and shrunken in the central acini. 



