154 LEO LOEB. 



constituent of the body fluids of the host and the strange cells and 

 that this interaction leads to the formation of toxic substances. 

 While these toxic substances probably interfere in an injurious 

 manner with certain sensitive tissues and lead to their destruction 

 in an indirect manner, in the case especially of certain epithelial 

 structures they merely alter the metabolism in such a way as 

 would be perfectly compatible with the life of the tissues. But 

 this alteration in metabolism sets into motion secondary processes, 

 in consequence of which lymphocytes, vessels and fibroblasts 

 show an altered relation to the transplanted epithelium and these 

 tissue reactions lead secondarily to the death of the transplant. 



SYNGENESIO AND HOMOIO TOXINS AS PRODUCTS OF METABOLISM. 



We have assumed that the substances which are characteristic 

 of the individual and which call forth the reactions which we 

 have described, pass into the surrounding medium as the result of 

 the metabolism of the tissue. In all probability they are not 

 merely decomposition products of proteins. In order to exclude 

 this latter interpretation we studied the behavior of the host tissue 

 towards homoiotransplantecl bloodclots in which the blood cells 

 live for a certain period without, however, carrying on an active 

 metabolism. We found that such blood cells do not call forth 

 any of the reactions characteristic of homoiografts ; neither 

 lymphocytes nor connective tissue nor vessels behave towards 

 them in any specific way whatever. These homoiodifferentials 

 are as far as we know, common to all the active tissues of an 

 organism. They are the same in the different organs of the same 

 animal. As we stated above, we could show this fact in the rat 

 by multiple simultaneous transplantation of different organs of an 

 individual into the same host. Under this condition all the organs 

 elicit proportionately the same individuality reaction, because the 

 relation between the individuality differentials of host and donor 

 is everywhere the same. Particularly the lymphocytic reaction 

 allows us to estimate this relationship of the individuality differ- 

 entials in an approximately quantitative way, as our syngenesio- 

 transplantations have shown. 



