158 LEO LOEB. 



grafted tissue is injured to so marked an extent, that a depression 

 in metabolism occurs and the quantity of toxic substances attract- 

 ing the lymphocytes and produced in the metabolism of the tissue 

 is much diminished. All this applies to the transplantation into 

 not nearly related species. If we transplant into nearly related 

 species, results are much better as has been established by W. 

 Schultz. It seems that in this case the tissues behave almost like 

 homoiotransplants. However it appears probable to me that a 

 comparative study which so far has not yet been made, would 

 show that even in this case the results are distinctly less good 

 than after homoiotransplantation. If we disregard the hetero- 

 transplantations into nearly related species, there is after hetero- 

 transplantations not a close connection between the results of 

 transplantations and the relationship of the species used. The 

 heterotransplanted tissues are all so near the minimal threshold 

 which just permits life for a short time, that various secondary 

 factor often become of more importance in determining the 

 duration of life and extent of proliferation of the graft than the 

 character of the species differentials. There exists, however, as 

 we have shown an indication that even here such a relationship 

 enters as one of the determining factors. 



SPECTRUM OF RELATIONSHIPS AND INTERACTION OF TISSUES. 



If we now compare the effect of the various kinds of trans- 

 plantations on the character of the interactions between the tissues 

 of host and graft, we come to the following conclusions : 



i. The autotransplants have the greatest degree of efficiency in 

 preserving the integrity of the graft and in maintaining inviolate 

 the boundaries of the organs and in preventing the ingrowth of 

 the connective tissue of the host. The autotransplant behaves in 

 this respect most like the normal organ. From there a decrease 

 in efficiency takes place if we pass to the syngenesio- and to the 

 homoiotransplants. In the heterotransplant this power of pre- 

 serving the integrity of the graft and of warding off the attack by 

 strange connective tissue has become very slight. There is, how- 

 ever, still noticeable a slight action of the transplanted paren- 

 chyma even in this case ; but on the whole the tissue behaves not 



