426 



K. G. DERNBY AND J. BLANC 



Gelatin tests 



In order to make all experiments in exactly the same manner 

 standard mixtures of gelatin and HCl or NaOH were made before- 

 hand, of which the hydrogen ion concentrations were known. 

 Table 5 shows the composition of these mixtm'es. 



As our aim was to study the optimum reaction, it was suf- 

 ficient for us to study the first stages in the liquefaction process. 

 During this early period the hydrogen ion concentration will 

 not change much, and buffers could be omitted. 



TABLE 5 



Composition of gelatin mixtures 



The gelatin solution contained 14 per cent gelatin and 0.4 per cent thymol. 



10 cc. gelatin, HCl, NaOH or HjO, 12 cc. 



In preliminary experiments it was determined how much of 

 the enzyme had to be taken in order to liquefy the gelatin within 

 4 to 20 hours at the optimum pH value 6.5. 



In all cases a set of seven tubes was used, covering a range in 

 pH from 3.0 to 9.0. Ordinarily 5 cc. gelatin were used for each test. 

 The tubes were warmed to 37° before the enzyme was added. 

 The gelatin contained 0.5 per cent thymol and the enzyme solu- 

 tion was aseptic. Therefore hardly any proteolytic activity from 

 other microorganisms need be taken into consideration during the 

 short time of digestion. A blank experiment was always run at 

 the same time. After certain intervals the tubes were taken 

 from the incubator and put into an ice bath for exactly ten min- 

 utes; thereafter the degree of liquefaction was estimated by the 

 method given in the paper by Dernby (1918). 



