46 



THE AM ERIC AX XATURALIST 



[Vol. LIV 



We found, however, that not only the lymphocytes, but 

 also the blood and lymph vessels and fibroblasts behaved 

 in a specific manner in accordance with the relationship 

 between host and graft. 



We assume that all the tissues of an individual have in 

 common a certain chemical group which may be desig- 

 nated as individuality-differential. After transplanting 

 a piece of an organ into a near relative of the donor of 

 the tissue ( syngenesiotrausplantat ion), or into an unre- 

 lated individual of the same species (homoiotransplanta- 

 tion), or into an individual belonging to a different 

 species (heterotransplantation), the individuality-differ- 

 ential is no longer adapted to its environment and acts as 

 a syngenesio-, homoio-, heterodifferential, respectively. 

 In this inadequate environment the individuality-differ- 

 ential assumes injurious properties, either directly or 

 after interaction with the body fluids, some protein con- 

 stituent of which contains likewise the individuality- 

 differential or rather a group specifically combining with 

 the individuality differential. It is probable that the 

 second alternative represents the usual way in which the 

 individuality-differential becomes a syngenesio-, homoio-, 



In certain cases the toxic character of the substance 

 which originates after homoiotransplantation is strong 

 enough to exert a direct injurious action on certain trans- 

 plantation is strong enough to exert a direct injurious 

 action on certain transplanted tissues, for instance, myx- 

 oid connective tissue and unstriated muscle. It can also 

 directly interfere with those metabolic processes which 

 lead to the production of epithelial pigment. In other 

 cases, however, the toxic substances, while strong enough 

 to modify the metabolism of the tissues, do not endanger 

 the life of the transplant. This occurs after transplanta- 

 tion of glandular structures like kidney or thyroid or 

 epithelial structures in general. But secondarily this 

 change in the metabolism of the transplanted tissue alters 

 the reaction of the host cells towards the graft. The 

 lymphocytes are attracted, the vascular supply is dimin- 



