GENERAL CONSIDERATIONS 33 



effective in inciting a lymphocytic reaction than is cartilage with the surround- 

 ing fat tissue. Likewise, transplants of striated muscle tissue may be infiltrated 

 with lymphocytes, when in other tissues lymphocytes are absent or much less 

 numerous ; but as a rule, also in the muscle tissue they are present in larger 

 masses only if there is a definite antagonism between the individuality differ- 

 entials of host and transplant. But lymphocytes accumulate very readily even 

 around dead foreign bodies such as threads, especially if these foreign bodies 

 are situated in tissues possessing an individuality differential which is not 

 quite compatible with that of the host. In cases of infection in the fat tissue of 

 the mouse, there may be found in addition to the accumulations of poly- 

 morphonuclear leucocytes, collections of lymphocytes, an increase in connec- 

 tive tissue and an infiltration of the fat tissue with small vacuolated epithelioid 

 cells; but similar cellular changes may be noted in this animal also if the 

 homoiogenous differentials of host and donor are sufficiently strange to each 

 other. In such cases we have to deal either with a summation of the effects of 

 incompatible individuality and organ differentials, or of the combined effects 

 of the former and of bacterial infection or foreign body action. These com- 

 plications by no means diminish to any considerable extent the value of the 

 lymphocytic reaction as an indicator of the relation of the individuality differ- 

 entials to each other even in the mouse, just as little as the value of the agglu- 

 tination reaction in serological tests is destroyed by the fact that also changes 

 in ion concentration in the medium in which cells or particles are suspended 

 may cause agglutination ; but it will be necessary to take all these factors into 

 account in evaluating the results of such experiments. 



In the large majority of our experiments we transplanted pieces of two or 

 more different tissues from the same donor into different places of the sub- 

 cutaneous tissue of the host and these pieces were subsequently removed at 

 the same time for examination. As a rule, it was then found that the kind and 

 intensity of the reaction of the host against these various tissues or organ 

 pieces were similar. In autotransplantation, injurious reactions were lacking 

 against all of them. In homoiotransplantation, if a severe reaction took place 

 against one of the pieces, all the others were likewise severely damaged; if 

 the homoiotoxins were less strong, the reactions in all pieces were equally mild. 

 In syngenesiotransplantation, corresponding reactions of a mild character 

 occurred in each case. In general, also the lymphocytic infiltration showed a 

 similar degree of intensity in the different grafts from the same donor into 

 the same host, provided the various complicating factors mentioned above 

 were taken into consideration. Likewise, the reaction against all types of 

 heterogenous tissues was of the same kind. In all these evaluations it is 

 necessary to make allowance for differences in the sensitiveness, the power of 

 resistance, the mode of growth of the tissues, and the amount of individuality 

 differential substances produced in the various types of transplants. We should 

 not expect the same reaction to take place against cartilage as against thyroid, 

 as each of these tissues has its own peculiar characteristics. Because of the 

 presence of so many variable factors present in investigations in which living 

 tissues enter into various kinds of relations, it is necessary to make in each 



