TRANSPLANTATION OF TISSUES IN MICE 55 



transplantation. Hemorrhages were observed in the thyroid transplant at 12 

 days, therefore at early periods after the operation, but they also had disap- 

 peared at 30 days. In one autotransplant of thyroid gland an abscess, due to 

 bacterial infection, adjoined the graft in one place; the ring of acini was 

 interrupted at this point, but this condition did not destroy the autogenous 

 character of the transplant except locally. In early periods following auto- 

 transplantation the amount of fibrous tissue in the center of the graft may be 

 considerable, owing to the organization of the central necrotic tissue ; but this 

 decreases later. In the transplanted fat tissue, infiltration with lymphocytes, a 

 noticeable increase in connective tissue, and the presence of small vacuolated 

 phagocytic cells are lacking. Localized necrosis of the cartilage may here also 

 be followed by the formation of a plate of new cartilage through the regenera- 

 tive activity of the perichondrium. We have not examined autotransplanted 

 mouse tissue later than 30 days following transplantation, but there were al- 

 ready some indications at this period that the effects of the accidental factors 

 we have mentioned disappear in the course of time as a result of regulatory 

 activities of the tissues, which take place under autogenous conditions. By a 

 comparison of the results of autogenous and homoiogenous transplantation it 

 is thus possible to separate a variety of more or less accidental factors from 

 the specific ones caused by the disharmony of individuality differentials. 



Homoiogenous transplantation. This 'consisted of two kinds of experi- 

 ments, namely, (1) an exchange of tissues between not closely related tame 

 mice or between non-inbred and inbred strains of mice, and (2) exchange 

 of tissues between closely inbred strains of mice. The second set of experi- 

 ments was first carried out, and in this type of homoiogenous transplantations 

 the connective-tissue as well as the lymphocytic reaction was definitely weaker 

 than in the corresponding transplantations in rats and guinea pigs. There was 

 the possibility that the relatively low intensity of these reactions was due to the 

 close inbreeding to which these mice had been subjected. We added, therefore, 

 to these transplantations, the first series; but here the results were similar, 

 indicating that these weak reactions are characteristic of the mouse and that 

 they are not due to the close inbreeding. If we make allowance for these differ- 

 ences, the grades in these transplantations in mice are otherwise in principle 

 the same as in the experiments with rats or guinea pigs. If the thyroid was 

 preserved, the relative incompatibility of the individuality differentials in host 

 and graft was indicated in many cases by the stunted condition of this trans- 

 planted organ; in addition, the organization of the central necrotic material 

 was, in some instances, as yet imperfect. There were a number of experiments 

 in which, particularly in the fat tissue, there were found either some scattered 

 polymorphonuclear leucocytes or even small collections of these cells. In such 

 transplants there were, as a rule, also an increased amount of fibrous tissue 

 and an increase in lymphocytes visible in addition to small vacuolated cells. 

 More rarely, a few polymorphonuclear leucocytes were found also in homoio- 

 genous thyroid or other homoiogenous transplants. As already mentioned, 

 there was often some doubt as to whether the presence of the leucocytes was 

 not due to accidental infections with bacteria, which could take place more 



