76 University of California Publications in Zoology [VOL. n 



poles fed on yolk of egg than among those fed on liver, the 

 tadpoles on lecithin mixed with other foods show a smaller per- 

 centage of deaths than the control lots receiving no lecithin. 



It has been noticed in the experiments with lecithin in con- 

 nection with other foods, that the color differences vary from 

 time to time. Such differences have been noticed in all the 

 experiments to a greater or less extent. In general the differ- 

 ence between the color of tadpoles fed on yolk and those fed on 

 liver is very noticeable at the end of the first week and continues 

 to be very marked until the larvae are about half grown, when it 

 becomes less distinct. From about the time the hind limbs 

 appear until the metamorphosis is complete, the color difference 

 is again marked. 



These differences are never great enough to suggest an actual 

 disappearance of pigment already formed, but rather a slight 

 difference in the rate of pigment production at different stages 

 of development. That is, the pigment production in tadpoles fed 

 on egg yolk or lecithin though at all times less than in the 

 tadpoles fed on liver may be greater at one time than at another. 

 It is possible that the tadpole at different stages of development 

 is differently influenced by the lecithin. The differences may be 

 more or less periodic, but more observations and histological data 

 are necessary for an intelligent discussion of this phase of the 

 problem. 



G. EFFECT OF CERTAIN OTHER ORGANIC SUBSTANCES UPON 

 THE TYROSINASE REACTION AND UPON PIGMENTATION 



A consideration of the effect of various other chemicals upon 

 the tyrosinase reaction is important if we grant that chemical 

 substances thus profoundly influence pigment formation. 



Abderhalden and Guggenheim (1907) found that n/100 

 hydrochloric acid inhibits the action of tyrosinase and n/100 

 sodium hydroxide retards it considerably. Neutralization of 

 acid or alkali fail to restore the original activity of the oxidase. 



Chodat and Staub (1907) observe that the oxidation of 

 tyrosin by tyrosinase is diminished by glycin, leucin, and alanin. 

 They find that tyrosin acts upon certain peptids such as tyrosin 



