TRANSPLANTATION OF SKIN 113 - ...:. •:..:.,.. ,...•/. •.,,.... ,..•.. .,:..• ..:..,..• ..•: ,:•...:,....:. . .. Figure 1. Heterotypic recombinant graft of 25 days' standing produced by placing a sheet of tongue epidermis on dermis prepared from pigmented ear of s•rain •2 guinea pig and transplan,ting it to a white skin ar• on the side of the chest of strain •2 host. At graft cen,ter there is conspicuous area of hyperkeratini•tion which overlies lingual epithelium (x •) hamsters (2). The dermal and epidermal moieties are separated, with the aid of trypsin, from thin shavings of different types of skin in ana- tomically intact and viable form. Epidermis isolated from one distinc- tive type of skin is then combined with the dermis of a different kind of skin and the recombinant graft is then transplanted to a bed of appro- priate size prepared on the trunk of a genetically compatible host-- another member of the same inbred strain as the donor (Fig. 1). This enables one to study the histogenic properties of one type of epidermis when it is sustained by an anatomically alien type of dermal stroma on a long-term basis. In the guinea pig, heterotypic recombinant grafts from ear, trunk, and sole of foot skin components, in various combinations, always express the specificity naturally associated with the derreal component. This favors the hypothesis that cells of the germinal layer of the integument are "equipotential" (11). However, epithelia from tongue or esophagus recombined with sole or ear dermis always retain their distinctive histo- logical characteristics indefinitely (Figs. 1 and 2). Likewise, the epider-

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