24 PIGMENTARY GROWTH AFTER ABLATION OF 



the fluids bathing these cells or, on the other hand, to alterations 

 in their nervous mechanism. 



Unimpeachable evidence has been secured on this point by 

 reciprocal skin transplants. In a very considerable number of 

 cases skin interchanges have been successfully effected between 

 a normal tadpole and its albinous mate. Invariably, and in a 

 period not exceeding four hours for the xantholeucophores and a 

 somewhat longer period for the epidermal melanophores,^* these cells 

 of the transplant assume the state characteristic for the corresponding 

 cells of the host. 



The technical manipulations involved in performing these skin 

 exchanges even in larvae exceeding 40 mm. in length are not 

 difficult. A narcosis sufficiently deep for operative work has not 

 readily been effected at room temperature, although serving 

 well for ordinary examinations in which no trauma was inflicted. 

 Of the several anaesthetics employed, ethyl eurethane (Merk) 

 in a strength of 0.5 per cent has proved the most efficacious, 

 especially when used at a low temperatxu-e (1° to 3°). The 

 lighter narcosis effective at this low temperature is of no 

 little significance, since not only is recovery more certain, but 

 also functional changes in the pigment cells inherent in a pro- 

 found anaesthesia are avoided. 



After a sufficiently deep insensibihty had been produced, the 

 specimens were placed closely together in depressions in the 

 wax plate lining the dish. Incisions on the dorsal epidermis 

 mapping out an area approximately 4X6 mm. were then made 

 on the dorsum of each specimen with the aid of the binocular. 

 Following this the skin was rapidly freed and the interchange 

 effected, the grafts being gently pressed down and not infre- 

 quently tucked under the edge of the host's skin. These grafts 

 quickly adhered, and in a short time no movement of the host 

 could dislodge them. 



" This reaction of the epidermal melanophores of the albinous graft to the normal 

 host— one of expansion— applies only to the cells originally belonging to the graft. 

 Epidermal melanophores from the surromiding normally pigmented epithelium 

 of the host quickly invade the albinous graft. These cells display a state of great 

 contraction for at least a considerable interval. 



