78 



Scientific Proceedings (97). 



his statements made in 1916. While it is impossible to attribute 

 more than a minor role to this, nevertheless, it is just as striking 

 and constant as the other pigment effects. This alteration in 

 the epithelial "free" pigment would appear to have escaped 

 detection along with the decided changes in the xantholeucophore 

 cells. Attention has already been called to the solvent action 

 of many fixatives on these cells. Their identification is not inter- 

 fered with by the use of Helly's fluid and is rendered easiest of all 

 when whole mounts preserved in this way are explored with the 

 polariscope with which the doubly refractive powers of the guanin 

 substance is brought out. It is proper here to call attention to 

 the fact that the maximal expansion which these cells enjoy in 

 albinous larvae can also be overlooked because of a subsequent 

 contraction in them which occurs with the use of anesthetics and 

 in many conditions of impaired vitality occurring through disease 

 or intentionally experimentally produced as with too strong doses 

 of adrenalin. In another place comment will be made on the 

 change in the physiological and pharmacological reactions of both 

 types of pigment cells; but it may be stated here that the widely 

 expanded xantholeucophores of albinos are singularly unamenable 

 to most experimental influences and in this they are in striking 

 contrast to the iridescent cells of normal animals. That the 

 expanded xantholeucophores contribute decidedly to the albinous 

 appearance is shown by the behavior of those albinous larvae fed 

 on posterior lobe substance. These animals exhibit a partial 

 recovery of the melanin deficiency which may indeed approach 

 the normal. In spite of this, they are always conspicuously lighter 

 than their normal controls, a fact readily explainable by failure 

 of this treatment to influence the persistent expansion • of the 

 iridescent cells. 



44 (1419) 



On the reaction of the pigment cells in normal and albinous frog 



larvae. 



By P. E. Smith (by invitation). 



[From the Anatomical Laboratory, University of California.] 



In the experimentally produced albinous frog larvae which 

 follow a successful early extirpation of the epithelial portion of 



