CHAR I.] ACTION OF SALIVA UPON STARCH. 41 



65 and 70. The salivary enzyme would appear to be influenced by 

 temperature exactly as the diastatic enzyme of the pancreas. 



influence of In the case of the diastatic enzyme of the pancreas 

 of 6 qwnttty Roberts has shewn that the amylolytic work done by a 

 presenToTthe gi yen solution containing it is strictly proportional to 

 amount of the quantity of it set in action ; in other words, the 

 starch con- amount of the standard starch mucilage which can be 

 verted. changed to the ' achromic point ' in a given time and at 



a given temperature, varies directly as the quantity of the solution 

 employed. This law appears to hold equally well in the case of the 

 salivary enzyme. 



influence^ of Within certain limits the time occupied in effecting 

 the quantity , c ,. . . , ... % 



of enzyme on the transtormation varies inversely as the quantity 01 



the time occu- the enzyme or enzymic solution, i.e. double the quantity 



pied in the of an enzyme; and the transformations will occur in 



transforms half th time 

 tion. 



The evidence When alcohol is added to a starch solution subjected 



of the existence to the action of ptyalin, or to that of any other diastatic 

 of various pro- ferment, at any stage of the process, there is thrown 

 down a precipitate which is composed of a mixture of 

 dextrins, whilst the filtrate contains maltose. At different stages 

 of the ferment-process, the solution exhibits changes in its power 

 of reducing cupric oxide (as determined by boiling a given volume 

 of it with Fehling's solution), and in its power of rotating the plane 

 of polarised light, the former increasing and the latter diminish- 

 ing as the process proceeds; similarly the products which can be pre- 

 cipitated at various stages differ in their reducing and rotatory 

 powers. 



In investigating the soluble products of the action of a diastatic 

 enzyme on a starch solution, at any particular stage of the process, a 

 known volume of the filtered solution is concentrated by evaporation in 

 the water bath, and absolute alcohol is then added in such proportion as 

 to furnish a mixture containing about 95 per cent, of absolute alcohol. 

 By this procedure the dextrins present are entirely precipitated, and their 

 amount determined by collecting them on a weighed filter, washing with 

 absolute alcohol, drying at 100C. and weighing. The alcoholic filtrate, 

 which contains the whole of the maltose, is evaporated to dryness, the 

 residue dissolved in distilled water, and the amount of sugar determined 

 (a) by Fehling's solution, preferably by weighing the oxide of copper 

 formed : (6) by means of the Polarimeter. The following is an example 

 (taken from a memoir by Dr Lea 1 ) which illustrates the accuracy with 

 which by careful experimenting, the amounts of the products can be 

 determined. 



1 Sheridan Lea, 'A Comparative Study of Artificial and Natural Digestion. 

 Journal of Physiology, Vol. xi. 1890, p. 234. 



