160 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



rapid an injurious effect was not observed in the case of transplanted tissues, 

 the importance of such toxins in transplantation was ruled out. The possi- 

 bility that in homoiogenous transplantation we may have to deal with primary 

 toxins of a different kind, acting less acutely but rather slowly in a gradually 

 cumulative manner, was not sufficiently taken into account. In the second 

 place the conclusion of these investigators, were based to a large extent, on 

 naked-eye observations of skin grafts and not on the microscopical examina- 

 tion of successive stages in the process of transplantation. The latter would 

 have revealed the fact that a reaction of the host may set in at a much earlier 

 stage than would have been otherwise expected ; the specific cellular reactions 

 of the host could begin as soon as the transplant had sufficiently recovered from 

 the injuries inflicted by the operation and by the transfer into a strange soil. 



The cellular reactions of the host against the transplant were likewise 

 attributed to immune processes which develop in the host. In the case of tumor 

 transplantations, cellular infiltrations were observed by Da Fano in various 

 places in the host ; these cells were lymphocytes, plasma cells and macrophages, 

 and they were interpreted by Da Fano as indicators of, as well as instruments 

 in the production of an active immunity against the transplanted tumor, and 

 also the numerous observations of Murphy as to the significance of lympho- 

 cytes around transplanted tumors were in harmony with this view. On the 

 other hand, we interpreted cellular infiltrations, principally of lymphocytes, 

 around and in the homoiogenous transplants as being caused by the difference 

 in the individuality differentials of host and transplants, these cells being at- 

 tracted by the strange individuality differentials of the grafted tissue; their 

 presence indicates the existence of variable degrees of incompatibility be- 

 tween tissues and the action of a mild rather than that of a severe, acutely 

 acting toxin. 



We tested, partly in collaboration with Cora Hesselberg, the effect of a 

 first transplant on a second transplant in several series of experiments in 

 guinea pigs and rats of different ages. The first transplants remained in the 

 host for periods varying from two to twelve days. Control experiments were 

 made for the first as well as for the second transplants. Single instead of 

 double transplants served as controls in some instances ; in others, a piece of 

 paraffin was inserted instead of a first transplant. In general, it may be stated 

 that no definite effect of the first on the second transplant was noticeable in 

 these experiments, the condition of both transplants varying within the same 

 range as those in the controls. If we assume that it was the development of an 

 immune state in the host which caused the reactions against the graft, we 

 should have expected that about eight to twelve days after transplantation of 

 the first pieces an immunity was established and that, accordingly, the lympho- 

 cytes were ready to attack the strange homoiogenous tissue. A definite lympho- 

 cytic reaction should therefore have developed around a second transplant 

 within the first five days after transplantation. This, however, was in no case 

 observed ; instead, the reaction occurred at about the usual time and as usual 

 there were considerable variations in the strength of the reactions against the 



