102 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



Strain A. In experiments in which the donors were from 14 to 19 months 

 old and the hosts were young, the transplanted thyroid was found more or less 

 sclerosed, which means that the individual acini were surrounded and sep- 

 arated from one another by hyaline-fibrous tissue. However, in strain A, begin- 

 ning soon after the age of 12 months, the thyroid normally undergoes sclero- 

 sis, although not so frequently as in strain C57. The parathyroid showed cor- 

 responding pericapillary hyalinization. It follows that these local tissue changes 

 cannot be reversed by transplantation into young hosts, where the constitu- 

 tion of the bodyfluids differs in certain respects from that in older animals. 

 While in certain cases some of these transplants behaved like autogenous 

 tissues, in some others the transplants were invaded by lymphocytes, slightly 

 or even more extensively. The lymphocytic infiltration became greater, espe- 

 cially around the grafts which had been kept in the host for longer periods. 

 This observation seems to confirm the conclusion that even in strain A the 

 individuality differentials of different animals have not yet become identical. 

 But, as we have found in other cases, here also local factors may co-operate 

 with the effects of a certain degree of incompatibility between the individuality 

 differentials in calling forth lymphocytic infiltration ; thus we noticed in one 

 instance in which two thyroids from the same donor were transplanted into 

 the same host, one showed some lymphocytic infiltration while the other one 

 was as yet free from it. Such a result may have meant merely that in one graft 

 the threshold of stimulation for the host lymphocytes was reached somewhat 

 earlier than in the other one. In reciprocal experiments, tissues (thyroid, 

 cartilage and fat tissue, striated muscle) were transplanted from 2 or 2y 2 

 months old mice to 18 or 19^ months old hosts. Here, all the tissues were 

 well preserved ; the transplants behaved on the whole like autogenous grafts ; 

 it is possible that the amount of preserved thyroid or muscle tissue was some- 

 what reduced, although this does not seem to be a necessary result of the old 

 age of the hosts. There was no sclerosis and no lymphocytic infiltration in the 

 old hosts. 



We compared with these intra-strain transplantations, inter-strain trans- 

 plantations of the same kinds of tissues, in which both host and donor were 

 about 4 to 5 months old. Here the reactions were much more severe. In some 

 cases the thyroid transplant had been entirely replaced by fibrous tissue and 

 lymphocytes, in others, more or less tissue had been destroyed. The average 

 grades in these inter-strain transplantations were: Strain A to strain New 

 Buffalo— 1.06; strain New Buffalo to strain A— 1.90. 



In strain D, in transplantations from young \y 2 to 2y 2 months old mice, to 

 mice ranging in age between 12 and 19 months, the grades varied between 3, 

 approaching grades given in autogenous transplantations, and 1+ ; usually 

 there was a partial fibrosis, due to increase of connective tissue between acini 

 and imperfect preservation of the transplants. In transplantations from 12 

 months old donors to 2 months old hosts the results were good, the grades 

 being mostly 3 and 3 — . In transplantations in which hosts and donors were 

 about 7 months old, the results were intermediate, lymphocytes invaded thyroid 

 and muscle and there were vacuolated phagocytic cells in the fat tissue. In 



