HETEROTRANSPLANTATION 121 



count of bacteria living on the normal skin seemed to be higher during the 

 hot summer weather than during other seasons. There was also some indica- 

 tion that the destruction of the bacteria proceeded more actively after hetero- 

 transplantation than after autotransplantation of the skin. 



The results in all these experiments make it probable that the poly- 

 morphonuclear leucocytes were attracted to heterotransplanted tissue not 

 mainly by bacteria attached to these tissues, but by the action of heterotoxins. 

 While it seems that this is, in general, the correct interpretation, still, under 

 certain conditions, and especially in transplantations carried out in the mouse, 

 it may well be that slight infections with microorganisms play a certain role ; 

 but it is probable that even if microorganisms should be involved, they act in 

 conjunction with toxins derived from the tissues and that they exert a greater 

 effect when the individuality differentials of host and transplant differ greatly 

 from each other than when they are closely related. 



We may further conclude that while the typical reaction against syngenesio- 

 and homoiotransplants occurs only if these tissues are alive and presumably 

 actively metabolizing, the heterotoxins are present and active also in dead 

 tissues. Additional evidence in favor of this conclusion is furnished by the 

 results of experiments in which the reactions of a host against autogenous, 

 homoiogenous and heterogenous blood clots were compared. If autogenous 

 and homoiogenous blood clots are transplanted into the guinea pig, the charac- 

 teristic differences that are found between the reactions of the host against 

 autotransplants and homoiotransplants of living tissues, such as thyroid, kid- 

 ney, epidermis, or cartilage and fat tissue, are almost or entirely lacking. This 

 seems to be due to the fact that the cellular elements enmeshed in the net of 

 fibrin soon die and no longer give off the autogenous and homoiogenous sub- 

 stances which bear the individuality differential. These clots are merely organ- 

 ized by the connective tissue and the blood vessels of the host like inert foreign 

 bodies, no noticeable amount of homoiotoxins being given off after trans- 

 plantation into another individual of the same species. As a result of the 

 invasion by the fibroblasts of the autogenous or homoiogenous host, first a 

 provisional organization takes place, representing a mixture of blood coagu- 

 lum and of the cytoplasmic substances of the fibroblasts; subsequently, a 

 definite organization is effected by continued ingrowth of fibroblasts. A few 

 lymphocytes may be admixed to the capillaries and fibroblasts, which move 

 into the clot, but they are not frequent. As stated, there are no definite differ- 

 ences between the autogenous and homoiogenous blood clots under these con- 

 ditions. While phagocytes may, to a limited extent, be seen in homoiogenous 

 blood clots, they are not a prominent feature in the process of organization. 

 The phagocytic cells distintegrate into granula, which later help to form a 

 hyaline material. Polymorphonuclear leucocytes are, on the whole, not con- 

 spicuous in these transplanted blood clots. It seems, then, that the non- 

 nucleated erythrocytes included in the network of fibrin do not give off 

 homoiotoxins to any noticeable degree. Much more pronounced was the re- 

 action against heterogenous blood clots, such as that observed if clots were 

 exchanged between rat, guinea pig and rabbit. In these cases, accompanying the 



