1913] Johnson: Pigment Formation in Amphibian Larvae 71 



Pepsin and pancreatin (Merck in both cases) were tested in 

 the same way, 0.2 grams being ground in 10 cubic centimeters of 

 water and the tyrosinase solution added. Pepsin inhibits the 

 reaction markedly, sometimes entirely. The pancreatin tubes, on 

 the other hand, are usually as dark as the control. 



Although, in these tests, liver inhibits the reaction more than 

 egg yolk, the result is reversed when the foods are digested, 

 digestion apparently lessening the inhibitory action of the liver. 

 As one would expect, whatever effects the foods may have on the 

 reaction before digestion, these effects are more or less changed 

 after digestion. 



SERIES B. DIGESTED FOODS 



In these experiments the foods were digested with pepsin and 

 pancreatin and the nitrates added to the tyrosinase solution. In 

 each case five grams of the food were ground in a glass mortar 

 with ten cubic centimeters of distilled water, and digested with 

 0.6 gram of pepsin or pancreatin. A few drops of toluol were 

 added and the tubes were kept in a warm place. After digesting 

 for forty-eight hours, the masses were filtered. The tyrosin and 

 tyrosinase were mixed and the solution measured out from a 

 burette into test tubes containing a few drops of toluol and 

 seven drops of filtrate or, in the case of the control, seven drops 

 of distilled water. 



By the time the solutions have been introduced into the tubes 

 containing the filtrates and toluol and the tubes arranged for 

 inspection they are all a delicate orange pink. The yolk tubes 

 soon become paler, passing into a pinkish white and the pan- 

 creatins soon lose the pink tinge entirely, passing into a light 

 greenish brown, at the same time turning a smoky black at the 

 surface. This black color gradually deepens until the solution is 

 jet black throughout. If after the reaction has gone on for 

 twelve hours, the tubes are shaken, the three are all very dark, 

 but the yolk tube is brown or greenish brown while the liver and 

 albumen tubes are jet black. 



The pepsin tubes go through the reaction more slowly, show- 

 ing much of the orange pink color after the pancreatin tubes 

 have lost their pink color and have become black at the surface. 



