414 INFLUENCE OF ACIDS ON THE 



EXPERIMENTAL. 



In the part following we shall attempt to demonstrate some 

 of the points just discussed, by extracts from the protocols of 

 our experiments. Our method has been similar to that of 

 Kiibel. Starch paste made from pure, neutral, arrowroot 

 starch; acid of known strength; and lastly saliva variously 

 diluted, have been mixed together, and the extent of amy- 

 lolysis at different temperatures determined after various in- 

 tervals (usually ten minutes). Kiibel's colorimetric method 

 was followed in estimating the relative rate of digestion. The 

 presence of free hydrochloric acid was tested for by the deli- 

 cate reaction with dimethyl amidoazobenzol first introduced 

 by Tb'pfer.* 



First Series. The experiments of this series illustrate how 

 the individual conditions may influence the limits of amylo- 

 lytic action independently of the quantitative relations of the 

 reagents which enter into the digestive mixture. They are 

 intended to contrast with Experiment 19 of Kiibel. As hi 

 his experiment, so here, a four per cent neutral starch paste 

 was used; mixed human saliva was diluted with one part of 

 water, filtered, and finally diluted with three parts of glycerine. 

 Different lots of saliva were employed. Under such condi- 

 tions Kiibel found with his own saliva and wheat-starch 

 paste that in a mixture containing five c.c. of starch paste, 

 0.3 c.c. of saliva, and five c.c. of acid of known strength, the 

 digestion at room temperature and during a period of ten 

 minutes was facilitated by hydrochloric acid of ^Vs to ?&s n 

 resultant strength, and entirely checked by ^ n or stronger 

 hydrochloric acid. In the typical protocols tabulated (Tables 

 A, B) it will be seen how the limits of digestive action may 

 vary with saliva from different sources, etc. It will also be 

 noted that digestion has not proceeded in those experiments in 

 which free hydrochloric acid was detected. 



The favorable action of very small quantities of acids (com- 



* Topfer, Zeitschrift fur physiologische Chemie, 1894, xix, p. 104. 



