1913] Johnson: Pigment Formation in Amphibian Larvae 69 



mum variation of 23 to 64 per cent for the same period of time. 

 There was no definite increase in size or weight in the increasing 

 concentrations of lecithin, nor was there a definite gain among 

 those in lecithin taken as a whole as contrasted with the controls. ' ' 

 These facts led to farther investigation of lecithin, its effect 

 both upon the tyrosinase reaction and pigmentation in the larvae. 



E. EFFECT OF LECITHIN AND VARIOUS FOODS USED IN EXPERI- 

 MENTATION, UPON THE TYROSINASE REACTION 



The following tests in vitro of the effect of the various foods 

 upon the tyrosinase reaction support the suggestion that the 

 lecithin in egg yolk inhibits pigment formation. 



Tyrosinase for the tests was obtained from different sources 

 as follows : 



(1) Ply larvae from six to ten days old were washed, chloro- 

 formed, and then ground with distilled water in a glass mortar. 

 The aqueous extract thus obtained was filtered through glass or 

 cotton wool, and used immediatel.y. This solution is a very 

 powerful one and turns orange pink throughout before one can 

 get it measured into the test tubes. 



(2) Meal worms were extracted in the same way and the 

 course of the reaction is much the same, but the solution does not 

 color quite as rapidly as in the case of the fly larvae. 



(3) Mushrooms were extracted with glycerine and water, 

 after having been ground in a glass mortar. The extract was 

 filtered through ordinary filter papers. 



(4) Potatoes were scraped and extracted with water for about 

 an hour. This extract was filtered through filter papers and used 

 as soon as possible. The solution is a pale orange pink by the 

 time it is measured out into the t&st tubes. 



A saturated solution of tyrosin in water was usually added 

 to these solutions for the experiments, but the extracts already 

 contained a chromogen since all of them darken after standing 

 for half an hour. Since solutions color up in the same way when 

 tyrosin is added as when it is not added, it seems likely that 

 tyrosin is the chromogen already present in the solution. The 

 extract from fly larvae gives a positive result for t.yrosin when 



