382 WILLIAM H. COLE 



Facts in the histories of the transplants in the LN, DN, LB and 

 LO series may be summarized as follows: 



1. Sixty-six per cent of all the tail-skin grafts over normal 

 eyes were partially absorbed in one way or another, allowing 

 light to reach the eyes. Complete union of the graft along its 

 edges delayed the absorption, and in 33 per cent probably pre- 

 vented it. Orientation of the grafts bore no relation to the proc- 

 ess, which was followed by a period of proliferation. 



2. Autotransplants and homoiotransplants of back skin over the 

 eyes showed neither absorption nor proliferation. Following the 

 healing period, they remained unchanged in size and shape. 



3. When the grafts of skin were placed on the back, not over 

 an eye, absorption never occurred. The origin and the kind of 

 skin made no difference in the results. Tail skin alone prolif- 

 erated. 



4. There was no absorption in grafts placed over empty sockets 

 or over eyes whose optic nerves had been cut. Nerveless eyes 

 rapidly degenerate, destroying the curvature of the conjunctiva. 

 Growth of tail-skin grafts proceeded as in the other series. 



These facts strongly suggested that the curvature of the eyes 

 over which the grafts are placed is a possible cause of the absorp- 

 tion process. Tail-skin grafts being composed of epidermis with 

 only a very thin dermal layer, are very plastic and respond to the 

 stimulus imposed upon them by the abnormal curved position. 

 If union is not complete or weak at some place, absorption occurs, 

 tending to restore the normal flat condition of the tissue. Some 

 transplants, because of their greater thickness or because of firmer 

 and more complete union than the others, resist the stimulus and 

 are not absorbed. This adjustment of the graft, however, must 

 take place before proliferation begins. At a certain time in its his- 

 tory the transplanted tissue undergoes a profound change, fol- 

 lowing which absorption is checked and proliferation is initiated. 

 Back-skin grafts, being composed of more compact tissue, with a 

 fibrous dermis, are not affected by the stimulus of abnormal posi- 

 tion or are not able to respond to it, and so are never absorbed. 

 This reasoning does not exclude, however, the possibility of a 

 functional cause for the absorption process. It was, therefore, 



