86 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



tissues between different litters of the same inbred family is entirely due to a 

 greater distance of relationship between these litters under these conditions, 

 although this factor may play a certain role, but that in exchange of tissues 

 between members of different litters the threshold required for a mitigated 

 reaction had not yet been reached in series I as well as in series II. In the case 

 of brothers and sisters it is probable that the decrease in the number and kind 

 of unlike genes which were present in different individuals helped to make the 

 individuality differentials so much alike that the reaction against the strange 

 individuality differentials was diminished. This increased similarity in the 

 constitution of the individuality differentials between brothers and sisters of 

 these inbred strains, which in many cases approached an autogenous state, was 

 brought out also in multiple simultaneous transplantations of various tissues 

 into the same host; here all the tissues behaved like autogenous transplants, 

 which is in accordance with the general rule that in transplantations from the 

 same donor to the same host, all tissues behave in the same way if we make 

 allowance for certain complicating factors, which we have discussed previous- 

 ly. Very instructive was also an experiment in which thyroids with adjoining 

 tissues were successfully grafted into brothers and sisters. After two successive 

 transplantations, and 50 days after the first transplantation, thyroid, para- 

 thyroid and fat tissue behaved like autotransplants ; but after the third trans- 

 plantation, the 73-day-old transplant showed a definite lymphocytic infiltration, 

 although otherwise it behaved like an autotransplant. 



This experiment confirms the conclusion that in series II a complete autog- 

 enous state has not yet been reached between brothers and sisters ; but on the 

 other hand, it is probable that a further progress, although a not very consider- 

 able one, towards a homozygous condition in families A and B has been made 

 in continued propagation by brother-sister matings in the interval between the 

 37th to 47th generations and the 60th to 67th generations. However, in addi- 

 tion the strength of the reaction may depend not only on the genes of the 

 donor, which are strange to the host, but also on the genes of the host, which 

 differ from those in the donor, although the importance of the strange host 

 genes is presumably less than of those of the donor. 



Series III. In this series, as a rule, thyroid, cartilage and fat tissue, as 

 well as pieces of striated muscle tissue, were transplanted and examination 

 took place 20 days later. Two groups of experiments were carried out. In the 

 first group ( 1 ) the hosts and donors were young rats, varying in age between 

 about one and three months. In the second group (2) the age of the animals 

 ranged between four and seven months. The results obtained in these experi- 

 ments are shown in table V. 



If we compare the transplantations in young rats (group (1)) and in some- 

 what older rats (group (2)), we notice that grafts between brothers and 

 sisters, in family A in group ( 1 ) , behave about like autotransplants, while in 

 group (2), they behave like good syngenesiotransplants. The transplants be- 

 tween different litters of the inbred family have grades corresponding to those 

 between good syngenesiotransplants; again, the grades are slightly better in 

 group ( 1 ) . A comparison with series I shows that transplants between differ- 



