SKIN TRANSPLANTATION IN FROG TADPOLES 373 



fection or other abnormal conditions. The behavior in all of 

 them was similar, absorption appearing in the second week, and 

 continuing, on an average, for seven days. When the process 

 stopped, the opening was about the size of the eyeball (fig. 13). 

 As a rule, then, absorption begins at any free place along an edge 

 of the graft. When there is no free place, it starts at the weakest 

 point on the line of union. When all edges are firmly and com- 

 pletely united, then the center of the graft, which is at the point 

 of greatest convexity and farthest away from the host, is the 

 starting-point of absorption. The place where absorption begins 

 is thus determined by the mechanical state of union between 

 the transplant and the host. 



It will be noticed from the foregoing description of the absorp- 

 tion process, first, that the amount was by no means constant, 

 varying from the maximum, which exposed the entire eye, to 

 that which produced only a small U-shaped area at a free place 

 without reaching the eye; and, secondly, that absorption usually 

 began before the close of the second week and came to an end 

 during the third week after the operation. There were only two 

 exceptions to this rule. LN 62 established complete union and 

 thereafter up to the fiftieth day showed no changes. At that 

 time it became loosened near the posterior ventral corner, and 

 absorption proceeded anteriorly along the ventral edge. After 

 a slight withdrawing of that edge, the process stopped and no 

 further changes took place (fig. 6). In the other case, LN 88, 

 with complete union, the middle of the anterior edge broke loose 

 on the thirty-second day. Absorption continued slowly until 

 the fortieth day, when one-half of the eye was exposed. These 

 two grafts were exceptions in another respect, since they never 

 showed any proliferation of tissue. There comes a time, there- 

 fore, in the history of the transplant, after which an adjustment 

 by absorption does not occur, and this time, according to aver- 

 ages, is about twenty-one days. It marks the close of the second 

 period. 



(3) Third or proliferation period. During the adjustment 

 period, the eighteen grafts which were not absorbed remained 

 without visible changes. Union had been established along all 

 edges. At about the beginning of the fourth week all transplants, 



