80 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



would be against two distinct transplants, one autogenous and the other 

 homoiogenous in nature. Two interpretations of this phenomenon are possible : 

 ( 1 ) it may be assumed that different structures after transplantation produce 

 and give off different quantities of the individuality differential ; thus cartilage 

 and fat tissue attract the lymphocytes in rat and guinea pig much less actively 

 than does the thyroid gland. There is reason for assuming that the metabolical- 

 ly less active cartilage substance produces a smaller quantity of individuality 

 differential per unit of time than does the metabolically more active thyroid 

 gland. However, this interpretation probably does not apply to the ovarian 

 structures; preserved follicles can hardly be less active in the production of 

 individuality differentials than is interstitial gland tissue, or even corpus 

 luteum tissue; (2) it is more likely that, in this and in other similar or even 

 more striking cases, as for instance, in adrenal gland transplants in mouse, in 

 addition to the individuality differentials certain tissue-specific substances 

 attract the lymphocytes; but at the same time it is probable that, in this in- 

 stance, also the individuality differentials play a role, their action being much 

 re-inforced by that of substances given off by certain types of cells and tissues 

 and not identical with the individuality differentials. It is conceivable that these 

 two substances — the individuality differentials and the tissue-specific sub- 

 stances — are chemically linked to each other and that this combination exerts 

 its influence on the lymphocytes, either directly or in conjunction with the 

 individuality differentials 1 circulating in the bodyfluids of the host. Such an 

 interpretation seems more probable than the assumption that the interaction of 

 the mutually not quite compatible individuality differentials of host and trans- 

 plant interfere more effectively with the metabolism of some types of cells 

 than with that of others, and that as the result of this interference, substances 

 are produced which attract the lymphocytes. In the transplant of the adrenal 

 gland of the mouse lymphocytes are attracted in large masses if certain re- 

 gressive, degenerative changes have taken place in the cortical cells, provided 

 this degenerative process does not exceed a certain limit. The rapidity and 

 frequency with which this regressive stage is reached in the cortical cells is 

 greatly influenced by the relationship between the individuality differentials of 

 host and donor. In addition to the interpretations mentioned already, after all 

 we cannot altogether exclude the possibility that in these cells larger amounts 

 of individuality differentials are produced than in the well preserved cortical 

 cells. Also to be considered is the possibility that in certain well preserved 

 tissues influences inhibiting the invasion of the lymphocytes may exist. These 

 are problems which still remain to be solved. 



(b) Syngenesiotransplantation in guinea pigs. As in rats, so we compared 

 in guinea pigs transplantations between brothers and sisters, from parents to 

 children, and from children to parents. In addition, transplantations from 

 grandparents to grandchildren and from grandchildren to grandparents were 

 carried out. The guinea pigs were either very young, as yet sexually immature, 

 or they were young adults ; also, the rats used in the experiments already re- 

 ported had been young. 



In the guinea pigs we carried out three series of experiments ; the largest 



