82 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



of blood vessels is very limited. But if there is no or only a slight accumula- 

 tion of injurious substances in this earlier period, then the connective tissue 

 cells form a myxoid connective tissue along the inner margin of the ring of 

 acinar tissue and there is here a good vascular supply. But in this case a 

 lymphocytic reaction may be expected to set in sometime during period II, 

 whenever toxic individuality differential substances produced have accumu- 

 lated in sufficient quantity to attract lymphocytes in larger numbers ; these 

 latter then invade the graft, perhaps together with a restricted amount of con- 

 nective tissue, which may move between and separate some of the acini. How- 

 ever, in general the severity of the reaction against the transplants increases 

 with increasing time following the grafting and the earlier syngenesio-reactions 

 may gradually become converted into severe homoio-reactions through 

 intensification of the fibrous-tissue reaction together with lymphocytic in- 

 filtration, both of these factors leading to an increasing destruction of the 

 transplanted thyroid. In cases in which paired organs from one donor were 

 transplanted to two brothers, or from a child to both parents, the reaction in 

 the two hosts was about the same in the majority of instances; this happened 

 especially in those instances in which the reaction was severe. Under these 

 conditions, a differentiation between results obtained in these hosts could not 

 very well be expected. However, sometimes the reaction differed in the two 

 hosts: there could be a severe lymphocytic reaction in the one and a slight 

 reaction in the other, and such a separation of the reactions occurred also when 

 the parents were derived from different strains of guinea pigs — one, for ex- 

 ample, being curly and the other smooth-haired. It was noted in such a case 

 that the reaction against tissues exchanged between parents and children was 

 severe, while on the contrary, there was some evidence that, when the parents 

 might have been related to each other, the reaction against the transplanted 

 tissues was relatively slight. In those instances in which two organs such as 

 thyroid and ovary were transplanted from the same donor into the same host, 

 the reactions against both organs corresponded to each other. 



In a general way, the grades were highest in the brother-to-brother (sister) 

 transplantations, and there was no distinct difference between the two re- 

 ciprocal types of transplantations when tissues were exchanged between 

 parents and children. Such a result might be expected when random trans- 

 plantations between non-inbred families of guinea pigs were carried out. In 

 the rat, no definite difference between the three types of syngenesiotransplan- 

 tation was noticeable. 



