92 R. E. BILLINGHAM AND WILLYS K. SILVERS 



Table I 



Median survival tlmes (MST) of homografts of normal trunk skin 

 exchanged between adult hamsters of different strains 



MST (days) 



Strain luith confidence limits Standard 



combination for 95% probability'^ deviation {days) 



C.B.->M.H.A. io-3±o-3 1-05 



C.B.->L.S.H. ii-5±o-4 I- 1 



L.S.H.->C.B. i3-3±o-8 i-2i 



* Estimated by the nomographic method of Litchfield (1949). 



indistinguishable from, those encountered in other species where 

 homografts confront their hosts with a whole battery of 

 "foreign" antigens. 



Structure and preparation of cheek pouch skin grafts 



The paired cheek pouches, whose highly vascular walls 

 constitute the milieu into which foreign grafts are implanted, are 

 elongate, highly distensible and evaginable diverticulae of the 

 buccal cavity employed by hamsters for the temporary storage of 

 relatively enormous volumes of food. The wall of the pouch 

 consists of: (i) a stratified epithelium several layers in thickness 

 and totally devoid of hairs and glands, firmly united to (2) a 

 relatively dense and well-vascularized layer of rather dense fibrous 

 connective tissue. Abundant longitudinal muscles are present 

 below this fibrous connective tissue near to the aperture of the 

 pouch. A fairly thick outer layer (3) of loosely packed areolar 

 tissue unites the pouch to the subcutaneous tissue of the cheek and 

 allows the entire pouch to be everted easily. A detailed account of 

 the structure and anatomical relationships of these organs has 

 been presented by Priddy and Brodie (1948). 



To obtain pouch "skin" grafts the organs were everted from 

 freshly killed animals, thoroughly cleaned with 5 per cent Dettol 

 solution, and then excised as close to their point of union with 

 the buccal cavity as possible. A longitudinal incision along one 



