68 University of California Publications in Zoology [VOL. 11 



It is quite possible that the two causes, perhaps three, always 

 operate to some degree, that a strong-pigment forming food such 

 as liver may furnish in the digestive process a large proportion 

 of tyrosin or some other chromogen, and at the same time fur- 

 nish few inhibiting factors. The third factor, not so easily 

 accessible to experiment, may be an increased formation of the 

 oxidase by a strong pigment-forming food. 



The large proportion of fat in egg yolk suggested that the 

 lecithin of the yolk might be the element that in some way 

 brought about a decrease in pigment production. The results of 

 Danilewsky supported the suggestion that lecithin might be an 

 inhibitor, possibly the only one. 



Danilewsky (1805) placed tadpoles in a solution containing 

 one part of lecithin to 15,000 parts of water. Other tadpoles were 

 kept in water alone to serve as a control. The former became 

 three times heavier and nearly twice as long as the corresponding 

 controls. He thought the effect was due to the stimulating effect 

 of the lecithin rather than to any great amount of nourishment 

 contained in it. He adds : * i II f aut encore noter que tous les 

 tetards lecithiniques etaient beaucoup moins pigmentes que les 

 larves de controle. " He found also that when lecithin is injected 

 into young rabbits or dogs there is a marked increase in their 

 growth. 



Miss King (1907) conducted a series of feeding experiments 

 with large numbers of toad tadpoles. She refers to an apparent 

 stimulating effect of lecithin in egg yolk and mentions meat as a 

 good pigment producer. 



Goldfarb (1910, p. 272) reviews the results of these and other 

 experiments with lecithin and reports upon similar investigations 

 of his own. He says, ''Frog and toad tadpoles were placed in 

 graded lecithin solutions ranging from one part of lecithin in 

 20,000 of water to toxic solutions of % and kept therein 

 throughout their period of metamorphosis (33 to 51 days) . Other 

 conditions, such as temperature, amount of solution, number of 

 tadpoles in each dish, food, etc., were constant for each series. 

 The control tadpoles showed at the end of the experiment a 

 variation of 9 to 53 per cent in weight, 3 to 44 per cent in length. 

 About 1,000 tadpoles kept in lecithin solutions showed a maxi- 



