412 INFLUENCE OF ACIDS ON THE 



alkalies, but apparently also by direct stimulation of the 

 ferment." * 



Kiibel employed a method introduced by Paschutin for the 

 estimation of relative amylolytic activity : at the end of each 

 trial digestion equal quantities of potassium hydroxide solu- 

 tion were added to the digestion mixtures, and the whole was 

 then plunged into a boiling water-bath for a definite interval. 

 In order to estimate more accurately the extent of digestive 

 action from the intensity of the yellow-brown color brought 

 about by the reaction of the caustic alkali with the soluble 

 products of amylolysis (Moore's reaction), Kiibel devised a 

 colorimetric procedure suggested by that of Griitzner for 

 pepsin determinations. Solutions of potassium bichromate 

 in various definite dilutions were employed for the color 

 comparisons. Although a method of this character is less 

 exact than direct quantitative determinations of the sugar 

 formed, it gives quite comparable results and makes it possible 

 to carry out a very large number of estimations at one time. 

 From such experiments Kiibel concluded that for a two per 

 cent starch paste, acids of -5^ n or weaker strengths consider- 

 ably facilitate the amylolytic action of human mixed saliva, f 

 Greater concentration of acid tends to inhibit the amylolytic 

 power, the degree of inhibition varying, for equimolecular 

 strengths, with the acids used. 



A comparison of Kiibel's work with the earlier investiga- 

 tions from this laboratory makes it evident that his conclu- 

 sions have for the most part been anticipated. Thus Chittenden 

 and Smith clearly demonstrated that small percentages of acid- 

 proteids tend to increase amylolytic action, and that a minute 

 trace oifree acid appears to facilitate the action still further. 

 Kiibel's results, while they are comparable with one another, 

 will not permit any general conclusion such as he has drawn 

 regarding the exact percentages of acids or alkalies which stim- 

 ulate or inhibit amylolytic activity ; for the work of previous 



* Chittenden and Smith, Studies from the Laboratory of physiological 

 Chemistry, Yale University, 1886, i, p. 83. 



t Kiibel, Archiv fur die gesammte Physiologic, 1899, Ixxvi, p. 303. 



