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THE AMERICAN NATURALIST [Vol. LIV 



those conditions which prevail in the case of allotrans- 

 plantation. Here they are prevented at most places from 

 breaking into the glandular structures; in the presence 

 of homoio- and hetero- and even of syngenesio-toxins they 

 tend in a higher degree towards the production of fibrillar 

 Lymphocytes are attracted by syngenesiotoxins and still 

 more by homoiotoxins ; here a maximum is reached. A 

 decrease occurs again in the region of the heterotoxins. 

 The number of fibroblasts invading the glandular trans- 

 plant is likewise greatest in the case of homoiotransplan- 

 tation. Again a decrease seems to occur in the case of 

 heterotransplants. 



We may express these facts also in a somewhat differ- 

 ent way. Under conditions of autotransplantation the 

 tissues give off substances which correspond to the iden- 

 tity of the individuality-differentials in the host and 

 graft. These substances, which may be designated as 

 "auto-substances," stimulate directly or indirectly the 

 vascular supply of the tissues belonging to the same indi- 

 vidual. And they also exert directly or indirectly a defi- 

 nite effect upon the fibroblasts, keeping them active and 

 preventing them from undergoing those processes which 

 probably represent a decline in normal metabolism and 

 which lead to the production of fibrous tissue at the ex- 

 pense of the healthy active cytoplasm. In the absence 

 of these auto-substances, the vascular supply is lessened 

 in direct proportion to the greater distance of the rela- 

 tionship between host and graft. To a certain extent 

 syngenesiotoxins still take the place of the auto-sub- 

 stances characteristic of the interaction between the own 

 tissues and body fluids. Some syngenesiotoxins however 

 can do so only to a very slight extent ; homoiotoxins are 

 still less able to take the place of auto-substances and 

 least of all heterotoxins. In the case of homoio- and 

 heterodifferentials the stimulating effect of the "auto 

 substances" is lacking; they behave in certain respects 

 like foreign bodies. 



On the other hand the autosubstances exert no attracting 

 influence on the lymphocytes, while the syngenesiotoxins 



