EXCHANGE OF TISSUES BETWEEN VARIETIES 135 



plantation, grade 1 signifies the complete destruction of a tissue of medium 

 sensitiveness, such as the thyroid gland, and the complete or at least very- 

 extensive substitution of fat tissue by fibrous tissue, the cartilage being pre- 

 served entirely or in part. But while in heterotransplantation the tissues are 

 injured to such an extent that regenerative growth does not as a rule occur, 

 this may take place in interracial transplantation. The reactions designated 

 by grade 1 have, thus, a certain latitude, signifying both the less severe and 

 the very severe injury inflicted, respectively, by interracial and by interspecies 

 (hetero) transplantations. 



