374 ENZYMES 



An absorption band will be observed on the yellow side of 

 the thallium line (571 - 54O//,//,). 



Another test for tryptophane consists in mixing the 

 suspected solution with a little glyoxylic acid and carefully 

 adding concentrated sulphuric acid so that the latter forms a 

 separate layer at the bottom of the test tube. After a short 

 time a purple ring is produced at the junction of the two 

 liquids, and on careful agitation the colour extends over the 

 whole solution. If pepsin be used in the above experiments, 

 it must be well washed in water and alcohol before use. 



QUANTITATIVE DETERMINATION OF THE ACTIVITY OF 

 PROTEASES. 



Schultz * followed the course of the action of pepsin on 

 egg albumen by precipitating out the albumen from time to 

 time and examining the optical activity of the peptone solution. 



Sjoqvist,f on the other hand, measured the electrical con- 

 ductivity of an albumen solution which was being hydrolysed 

 by pepsin.J 



Sorensen found that he could obtain a measure of the 

 amount of protein hydrolysed, by determining the number of 

 free carboxyl groups in the mixture. By adding an excess of 

 formalin, the free amino groups were neutralized ; the car- 

 boxyl groups were then estimated by adding an excess of N/5 

 baryta solution and titrating back the excess by means of 

 hydrochloric acid. 



ZYMASE AND ALCOHOLIC FERMENTATION. 



The formation of alcohol from fluids containing sugar has 

 been known and practised for thousands of years, and the use 

 of yeast in the manufacture of alcoholic beverages and of bread 

 is an ancient industry. As is well known, when yeast is placed 

 in a sugar solution, fermentation begins sooner or later, the 

 principal end products being alcohol and carbon dioxide; 

 substances other than ethyl alcohol, however, are formed, 



* Schultz : " Zeit. phys. Chem.," 1885, 9, 577. 



fSjoqvist: " Skand. Arch. f. Physiol.," 1895, 5, 317. 



JCf. Bayliss : "Arch. Sciences Biol.," St. Petersburg, 1904, u (supplem.). 



Sorensen : " Biochem. Zeit.," 1908, 7, 45. 



