DIFFERENTIALS IN CLOSELY INBRED MICE 99 



direct parents to the hybrids, although it still falls into the range of nearly 

 related individuality differentials. Decidedly more unfavorable were trans- 

 plantations from hybrids (C57xD)Fj to their own parents, with an average 

 grade of 1.42 in ten transplantations, or from such hybrids to members of 

 their parent strains, other than their actual parents, with an average grade 

 of 1.50 in five transplantations. Both of these reactions fall into the range 

 of homoiogenous relationship of the individuality differentials. In all these 

 experiments examination as a rule took place 20 days following trans- 

 plantation, and each mouse received transplants of thyroid, cartilage, fat 

 tissue and striated muscle ; whenever possible, also ovaries were trans- 

 planted. These grades indicate very strongly that neither in strains C57, D, 

 New Buffalo, nor even in strain A, has an autogenous condition of the 

 individuality differentials been reached ; but it has progressed farthest in 

 this direction in strain A. All these grades fall into the range of syn- 

 genesiotransplantation. However, the reactions are much milder in intra- 

 strain than in inter-strain transplantations, where they correspond to 

 homoiogenous transplantations. In accordance with expectation, the reactions 

 were more severe if instead of transplanting within the same inbred strain, 

 we transplanted between hybrids such as DxC57)F 1 , in which both parents 

 were from inbred strains. In this case the results were intermediate be- 

 tween those obtained in simple inter-strain and intrastrain transplantations, 

 corresponding to unfavorable types of syngenesiotransplantation. How- 

 ever, if the hybrids which served as donors and hosts were brothers and 

 sisters, then the results approached more closely those obtained in autog- 

 enous transplantations. As was to be anticipated, in transplantations from 

 parent strains to hybrids the grades were higher than in the reciprocal 

 transplantations. In the former, they corresponded about to the grades of 

 simple intra-strain transplantations, although they were slightly better 

 than the latter if the actual parents of the hybrids served as donors ; how- 

 ever, an autogenous condition had not yet been reached. The reciprocal 

 transplantations from hybrids to parent strains or to the actual parents 

 gave results which were only slightly better than those obtained in inter- 

 strain transplantations. 



As stated on previous occasions, in the mouse the main reliance in the 

 grading must be placed on the state of preservation of the various tissues, on 

 the kind of structures which survive, and on the extent of the ingrowth of 

 connective tissue into the various transplants and the degree of replacement 

 of the latter by fibrous tissue. In the case of the fat tissue, also the number of 

 epithelioid phagocytic cells which separate the fat cells is significant. While 

 lymphocytic infiltration plays a certain role likewise in the mouse, and while 

 it may be very intense in some instances, it can not be relied upon as a quanti- 

 tative standard in the evaluation of the reactions to the same extent as in rat 

 and guinea pig; but in the mouse, also, there is a very good correspondence 

 beween the fate of various kinds of tissues transplanted from the same donor 

 into the same host, if we make allowance for peculiarities of different types 

 of tissues and for accidental variable factors which may complicate the results. 



