DIFFERENTIALS IN CLOSELY INBRED MICE 113 



here at very late periods. This fact again seems to confirm the conclusion 

 that the individuality differentials in these inbred strains have not yet reached 

 an autogenous condition. 



Transplantation of the thyroid and parathyroid glands for longer periods 

 of time in various strains of mice and the analysis of the individuality differ- 

 entials. These experiments were made in addition to earlier transplantations 

 of the thyroid gland, which we have reported in the preceding pages, and in the 

 large majority of which the examination took place at earlier periods, usually 

 between 12 and 30 days following transplantation. 



In strain A, seven transplantations of thyroid and parathyroid, either alone 

 or in combination with other organs, were made ; examination took place 

 between 9 and 15 months, mostly between 10 and 11 months, following trans- 

 plantation. The thyroid and parathyroid glands were well preserved, although 

 there was in some instances a small amount of fibrous tissue around some 

 acini. In or around all transplants, except one, there was definite lymphocytic 

 infiltration, which was moderate in some cases and marked in others. This 

 also occurred in a case in which donor and host belonged to the same litter. We 

 may then conclude that an autogenous relationship between the individuality 

 differentials has not yet been reached and that the absence of lymphocytic 

 infiltration at a given time, indicating apparent compatibility between the 

 individuality differentials of host and transplant, does not actually prove such 

 a harmonious condition ; it merely indicates a lack of incompatibility great 

 enough to cause a lymphocytic reaction at a particular time, but does not ex- 

 clude the possibility that if the transplants had remained in the host for longer 

 periods, such a reaction would have occurred. 



In strain D, thirteen transplantations of thyroid and parathyroid were made ; 

 in all but four cases the organs from brothers and sisters were used. In two of 

 the animals from different litters no transplants were found 9 months after 

 transplantation. In the two remaining animals from different litters, 8 months 

 and 20 days, and 4 months after transplantation respectively, the structure 

 of the transplants was not like that of autogenous grafts and here was much 

 lymphocytic infiltration. In the nine cases in which donors and hosts belonged 

 to the same litter, the examination took place in most instances about 9 and 

 11 months after transplantation; in one, the time of examination was about 

 4 months, and in another it was 1 month and 3 weeks. In only two of these 

 transplants, namely in those examined after 9 months, was the lymphocytic 

 infiltration lacking; in seven grafts it was moderate or marked, but in every 

 case quite definite. These experiments confirm then again the conclusion, that 

 a homozygous condition did not exist in strain D. We may add that this is due 

 not merely to an early branching-off of sublines from the main line, because 

 late reactions occurred also between brothers and sisters, therefore between 

 members of this strain, which have been propagated continuously and directly 

 by brother and sister matings. In both strain A and strain D, antagonistic 

 reactions of the hosts may thus develop against tissues which had been trans- 

 planted a considerable number of months previously. 



In strain C57 the grafts remained, in eight cases, from 2 to 8>2 months in 



