1907.] Implantation of Actively Proliferating Epithelium. 551 



that by the 31st day the epithelium was considerably reduced in amount, and 

 that, as in normal skin, division figures were rare. The epithelium still 

 surviving at this period resembled normal surface epithelium, consisting of 

 a flattened expansion of prickle cells, covered with epidermic scales and 

 lying upon a bed of fairly dense connective tissue. No hair follicles or 

 sebaceous glands were seen at this period. Subsequently the epithelium 

 surviving became very scanty in amount. 



When the normal skin of the rabbit's ear was used for implantation 

 (Table II), after the lapse of about a month, the appearance of the portions 

 implanted was similar to that of the former series at the end of the same 

 period of time. 



In implanted skin a variable amount of the prickle layer always died. 

 Polynuclear leucocytes appeared in large numbers about the dead portion, 

 which could be readily recognised by the shrivelled character of its nuclei, 

 which stained imperfectly and diffusely. Not unfrequently dead and living 

 prickle cells lie close together, the latter showing numerous mitoses and 

 spireme figures. Subsequently the polynuclear cells were accompanied, and 

 later, for the most part, replaced by large mononuclear cells with abundant 

 cytoplasm (cp. figs. 5 and 7), before which the prickle cells gradually 

 disappeared, so that ultimately the place of the latter was occupied by large 

 mononuclear cells accompanied by multinucleated giant cells, the nuclei of 

 which lay chiefly in the centre of the cell (cp. figs. 6, 7, and 8). As in such 

 cases the horny epidermic scales still persisted unaltered, acting like inert 

 bodies, as did also the hair shafts (figs. 7 and 8), it might at first appear as if 

 these large mononucleated cells and giant cell masses were really epithelial 

 cells, which, owing to their changed environment, had undergone meta- 

 plasia, losing their prickles and their capacity for undergoing conversion into 

 keratin. That this is not so, however, was shown by the experiments of the 

 third series, in which the implantation of alcohol-hardened skin led to 

 precisely the same appearance of large mononuclear and giant cells, before 

 which the prickle layer disappeared (fig. 8), while the appearance of mono- 

 nuclear cells was preceded by that of polynuclear leucocytes, just as in the 

 first two series. This action of dead sterile epithelium in attracting poly- 

 nuclear leucocytes shows that the presence of the latter is not necessarily 

 due to contamination with bacteria. No evidence of the presence of bacteria 

 in the area of implantation could be obtained by staining methods, and the 

 appearance of the site of implantation was that of a purely aseptic process. 

 In this connection it may be observed that, when the normal skin of the 

 rabbit's ear was used for implantation, the same appearance of polynuclear 

 leucocytes at first, and later of mononuclear and giant cells, occurred. Fig. 6 



2 R 2 



