752 



THE AMEBIC AN NATURALIST [Vol. XLV 



duced was separated by filtration, redissolved in alco- 

 hol and acetic acid, and reprecipitated several times, 

 and finally used in 30 per cent, alcohol containing one 

 tenth per cent, acetic acid." Into this solution were 

 suspended pieces of primary cuticula, taken before pig- 

 mentation had begun to develop. "The result was that 

 in about thirty-six hours the cuticula had become brown, 

 being first drab, then pale brown, then full brown. Be- 

 yond this, coloration did not advance. It was uniform 

 over the entire surface, but, although areas where spots 

 normally develop were present, no tendency to spot for- 

 mation was observed." 



This does not prove that the solution which Tower 

 prepared contained enzymes, for the pieces of unpig- 

 mented cuticula which were used as the testing material 

 may have contained sufficient enzymes to produce the 

 pigmentation. Tower does not mention that he used a 

 check of distilled water in place of the "enzyme" solu- 

 tion. I have repeated this part of the work, and for the 

 piece of the primary cuticula I have used the fresh ely- 

 tron, taken before the pigmentation had begun to de- 

 velop. I find that there is an appreciable difference in 

 the rate of the development of the pigment when the 

 elytron is placed in the "enzyme" solution or in distilled 

 water, and that this difference is in favor of the dis- 

 tilled water. The color is distributed more over the en- 

 tire surface in the case of the enzyme solution, but I find 

 that this is probably due to the fact that the precipitate 

 contained some of the chromogen and when this came 

 in contact with the tyrosinase on the surface of the ely- 

 tron, pigment was produced. Tower's "enzyme" solu- 

 tion, if it does contain an enzyme, does not contain the 

 CHii/nie n-hich causes the pigmentation, for it gives none 

 of the tests for oxidases. Oxidases are destroyed by 

 solutions that are slightly acid so that this is probably 

 one of the reasons why his preparations did not give 

 more positive results. Another reason could be found 



