SKIN TRANSPLANTATION IN FROG TADPOLES 385 



period of equilibrium showing no changes during the time of 

 observation, which averaged 120 days. 



It might be said that the absorption of the tail-skin grafts over 

 artificial eyes was caused by the presence of foreign material 

 beneath them. To test this possibility, the hemispheres of glass 

 or celloidin were replaced by thin squares of glass cut from the 

 ordinary cover-slip. Otherwise the operations were the same as 

 those in which the hemispheres were used. Even in such grafts 

 slight curvature cannot be avoided. The glass laid on the square 

 of skin inside the incision raises the graft shghtly above the sur- 

 rounding integument. When the edges of the graft begin to 

 unite with the surrounding skin, they are pulled downward. 

 This downward pull on the edges causes a noticeable curvature 

 of the graft. In 40 per cent of these grafts (four out of ten cases) 

 absorption occurred and the glass was liberated. The liberation in 

 two cases was no doubt facilitated by the sharp corners of the 

 glass pressing against the graft. Six grafts showed no absorption, 

 the glass remaining buried. The eight back-skin transplants of 

 this sort were not absorbed, the glass remaining permanently 

 underneath. From these experiments, it was concluded that the 

 presence of foreign material beneath the graft was not the cause 

 of absorption of tail skin, but that the curvature of the graft was 

 the cause. In order to eliminate curvature of the graft entirely, 

 all of the integument within the incision must be removed. 

 When this was done and the thin square of glass placed in the 

 wound was covered by tail skin, no absorption occurred. The 

 grafts do not react to foreign material. Their only activity is 

 proliferation. Flat grafts in any region have never been ab- 

 sorbed. Kendall ('16), reporting on the use of frog skin to cover 

 slowly healing wounds in human subjects, says that the ideal 

 wound to graft is fiat. He found that grafts over curved sur- 

 faces were usually unsuccessful. In addition to the curvature, 

 the action of the heterotoxin produced in such grafts must also 

 hinder the establishment of union. 



The adjustment of a skin graft over an eye is therefore deter- 

 mined by the curvature of that organ. Artificial eyes produce 

 the same behavior as normal functional eyes. The incidence of 



