HAMSTER CHEEK POUCH SKIN HOMOGRAFTS lOI 



suggesting that the previous exemption of such grafts from rejec- 

 tion may have turned upon the absence of an adequate afferent 

 pathway for the immunological reflex mechanism. 



Various attempts have been made to bring about the destruction 

 of long-established homografts of pouch skin by subjecting them 

 to treatments considered likely to promote or enhance the escape 

 of transplantation antigens from them. These included topical 

 application of irritants, such as turpentine/ acetone mixture, and 

 croton oil, every third day over a period of several weeks. 

 Although both agents seemed to increase the blood flow through 

 the grafts and considerably increased the mitotic activity of their 

 epidermis, they were completely ineflective in promoting rejec- 

 tion. The weekly injection of 0-25 ml. of a physiological saline 

 solution containing 10 mg. hyaluronidase/ml. (i mg. = 691 

 U.S.P. units) via a No. 30-gauge needle very superficially into the 

 connective tissue of established pouch skin hom^ografts, where it 

 produced transient blebs, was also found to be ineffective. 

 Surgical trauma too was innocuous, as evidenced by the con- 

 tinued survival of the injected grafts just described, and the fact 

 that many established pouch skin homografts survived the con- 

 siderable traumatization accompanying the central inlay of skin 

 homografts. 



It is very difficult to explain the wide range of survival times 

 of pouch skin homografts displayed in each of the three donor/ 

 recipient strain combinations tested. How is it that whereas some 

 grafts were rejected just as quickly as homografts of normal skin 

 others survived indefmitely ? Genetic variation within the strains 

 can be excluded as a contributory factor since each strain is iso- 

 histogenic and reacts with complete uniformity to homografts of 

 ordinary skin. Two other possibilities are : 



(i) When cheek pouch skin homografts are transplanted they 

 carry over a variable number of donor strain leucocytes in the 

 small amount of blood remaining in their vessels. Sometimes a 

 sufficient dosage of these cells may survive the transient ischaemia 



