No. 540] 



STUDIES ON MELANIN 



751 



material, as almost all of the best of it was in sublimate- 

 acetic-acid fixation, which does not fix zymogens well, but 

 dissolves them and leaves vacuoles where the granules 

 should have been. . . . With Berenyi and picric acid 

 mixtures some zymogen granules were preserved, but 

 the rest of the material was so bad that the preparations 

 were useless. The account of the zymogens and their 

 part in pigmentation is based on material from L. 

 decemlineata and C. femorata. For demonstrating the 

 presence of substances, probably zymogens, I used iron 

 hematoxylin, which is fairly good, and Bensley's stain 

 for zymogens." 



I do not know by what right one can designate a 

 stained granule as a zymogen when we do not know 

 whether zymogens exist as distinct bodies or not. Zym- 

 ogen is only a term which we use to state the fact that 

 in some cases there is, apparently, the sudden appear- 

 ance of enzyme action where no enzyme action could be 

 previously detected. We call the mother substance of 

 this enzyme a zymogen, but since the term "enzyme" is 

 only another term for a peculiar kind of energy, which 

 may some day be shown to be only a catalysis, or other 

 physical phenomenon, we have, at present, no basis for 

 believing that either enzymes or zymogens can be stained 

 by definite stains. 



Tower states that lie has prepared an enzyme which 

 is responsible for the production of pigment, and which 

 causes the hardening of the primary cuticula. To this 

 "enzyme" he has given the name "chitase." The 

 method of preparing this enzyme is given on page 60 

 (1903), and on page 138 (1906). Pupa} were ground with 

 quartz sand and the mixture extracted with 35 per cent, 

 alcohol containing 2 per cent, of acetic acid, or with 50 

 per cent, alcohol containing 10 per cent, of glycerol. 

 "Dilute alcohol and acetic acid served the best, as it gave 

 the largest precipitate upon the addition of 95 per cent, 

 alcohol. The white, rather flocculent, precipitate pro- 



