SKIN TKANSPLANTATION IN FROG TADPOLES 405 



may result in abnormal pigmentation. By the rubbing or in- 

 jection of various substances, such as paraffin oil, xylol, agar- 

 agar, olive oil, and sudan III, into the skin of guinea-pigs, rabbits^ 

 and rats, a hypertrophy of the skin was produced, accompanied 

 by an increase in the pigment content (Brosch, '00; Ribbert, '04; 

 Fischer, '06; McConnell, '07). Schultz ('12) described a case of 

 excessive pigment formation of inflammatory origin in human 

 skin. He observed that the chromatophores, as well as other 

 kinds of cells, were stimulated to prohferate. It seems from these 

 results that whenever skin cells are stimulated to multiply at a 

 rate considerably above normal, pigment formation is increased 

 at a still greater rate. In spite of many attempts to explain such 

 reactions, an account satisfying all the known conditions remains 

 to be given. The possibihty that sarcomatous pigmentation is 

 due to stimuli fundamentally similar to the appearance of pig- 

 ment cells following an injury to the conjunctiva is merely sug- 

 gested here without drawing any conclusions. More evidence on 

 the whole subject of hypertrophy of integument and chromato- 

 phores is necessary. 



GENERAL SUMMARY AND CONCLUSIONS 



A . Mechanical adjustment of grafts over eyes 



1. Over the eyes of tadpoles of Rana catesbeiana and R. clami- 

 tans varjdng in length from 20 to 100 mm., opaque skin was 

 transplanted in a manner calculated to demonstrate the existence 

 of any regulatory interaction between graft and eye tending to 

 restore the function of the eye. 



2. In 66 per cent of the operations in which tail skin was placed 

 over the eye, the grafts were absorbed in a way which tended to 

 expose the eyes. Back-skin grafts over the eyes were never so 

 absorbed. 



3. Tail skin and back skin placed on other parts of the body 

 were never absorbed. 



4. Tail-skin grafts over hemispheres of glass or celloidin ('arti- 

 ficial eyes') were absorbed in the same way as grafts over normal 

 functional eyes. Back-skin grafts so placed were not absorbed. 



