106 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



of repeated retransplantations be diminished; this may perhaps lead to a 

 diminution of the injury inflicted on the grafted tissue. 



It is very probable that a sclerosed thyroid does not produce thyroxin and 

 is therefore functionally inactive, and it may be also that such a thyroid 

 produces a smaller amount of the individuality differential substance ; this con- 

 dition would tend to diminish the invasion of the transplant by lymphocytes. 

 Accordingly, we found the lymphocytic infiltration in these serial transplan- 

 tations of thyroid gland either lacking or slight; but, the fact that the indi- 

 viduality differentials in strain A approach, although they do not quite attain, 

 an autogenous state would in itself be sufficient to account for a lack of 

 lymphocytes. However, in the preceding experiments we noticed that after a 

 single transplantation of the thyroid gland, a sclerosed organ could be infil- 

 trated quite markedly with these cells. There is reason for assuming, then, 

 that in the case of the thyroid gland a deficiency in the amount of hormone 

 produced by the host thyroid is not required for a successful transplantation 

 of this organ, and, correspondingly, it is doubtful whether the diminution in 

 function of the sclerosed thyroid renders its transplantation easier. 



Transplantation between nearly related individuals in inbred strains of mice. 

 If the inbreeding in mice had led to a completely autogenous condition of the 

 individuality differentials among all the members of a closely inbred strain, 

 there should be no difference between the results of transplantations between 

 nearly related mice — namely, those which belong to the same litter and their 

 own parents — and between other mice which belong to different litters. They 

 all should show autogenous reactions. We carried out, accordingly, a con- 

 siderable number of experiments in which we studied transplantations of 

 various tissues, but especially of thyroid, cartilage and fat tissue, between near 

 relatives, and those between brothers and sisters. 



From these experiments it may be concluded that in brother-to-brother 

 transplantations, autogenous reactions predominated in all strains, and to the 

 highest degree in strains A, C3H and CBA ; but syngenesio-reactions did occur, 

 even in strain A, although they were more frequent in strains D and C57, and 

 in the latter strain even one homoiogenous reaction was noted, with some in- 

 crease in fibrous tissue. Variations in the age of the hosts within the range of 

 2 and 6 months did not seem noticeably to affect these results. The syngenesio- 

 transplants were characterized especially by an increase in lymphocytes, which 

 could destroy even otherwise autogenous tissue ; but there could be associated 

 with this reaction a slight increase of fibrous tissue. It was observed also that 

 transplantations from one donor to two hosts, or from two donors to one host, 

 might elicit somewhat different reactions. We note, then, that even in brother- 

 to-brother transplantations a complete identity of the individuality differentials 

 in these inbred strains has not yet been attained, and that again differences 

 exist in this respect between different strains. But there are indications that in 

 transplantations between litter mates the average of the reactions approaches 

 somewhat more completely the autogenous type than in transplantations be- 

 tween non-litter mates ; this seems to be the case, in particular, in strains D 

 and C57. In all these transplantations there was, as a rule, a correspondence 



