TRANSPLANTATION AND INDIVIDUALITY. 149 



proper and destroy them. Other lymphocytes approach the 

 thyroid from the periphery and from here push forward in a 

 central direction. All these lymphocytes surround, invade and 

 destroy the thyroid tissue directly after homoiotransplantation 

 and they are, therefore, the chief agent of destruction. They 

 interfere with the nourishment of the acini by surrounding them 

 and cutting them off from the vessels ; they exert furthermore a 

 direct pressure upon them and invade and substitute them. In 

 addition the fibrous tissue which is so prominent after homoio- 

 transplantation also tends to shut off the nourishing material 

 from the vessels. Furthermore it compresses the glandular struc- 

 tures and fibroblasts occasionally invade them, as we have stated 

 above. These lymphocytes and fibroblasts form, therefore, an 

 agency of attack which usually succeeds in destroying the homoio- 

 transplant of the thyroid somewhere between the fifteenth and 

 twenty-eighth day following transplantation. 



We may again assume that in the strange host the body fluids 

 are not completely adapted to the transplanted gland structures. 

 In consequence their metabolism is to a certain extent altered. 

 This alteration, however, is not of sufficient intensity to cause a 

 direct destruction of the transplanted glandular structures. This 

 alteration in metabolism attracts the lymphocytes, diminishes the 

 vascularization of the transplant and increases the invasion of 

 the graft by fibroblasts, which, however, under these altered con- 

 ditions do not remain intact, succulent cells, but instead form 

 fibrillar and dense fibrous tissue. 



In principle it is similar after transplantation of the kidney ; 

 but the greater denseness of this material brings about certain 

 minor modifications in the result. Thus in the kidney after auto- 

 transplantation we do not find the inner ring of lymph and blood 

 vessels so noticeable as in thyroid autotransplant. But in all 

 essential respects the conditions are parallel to those after trans- 

 plantation of thyroid. The formation of fibrous tissue is much 

 more prominent after homoiotransplantation of the kidney than 

 after autotransplantation. The lymphocytes play here a similar 

 part. In the end the homoiotransplant is again destroyed in the 

 same way as in the case of the homoiotransplanted thyroid. But 

 this destruction of the kidney may be completed at a somewhat 



