191 1] William J. Gies 315 



may have fallen. When starch paste is treated with a moderate 

 excess of very dilute acid Solution and the mixture is warmed, 

 certain conditions are instituted which greatly increase the affinity 

 between the colloid and the water, hydration is effected to the point 

 of hydrolytic cleavage, and soluble starch, dextrins and sugars are 

 progressively produced. When saliva is substituted for such an acid 

 Solution, similar products are formed, without the aid of heat and 

 in a much shorter period of time. This suggests that salivary diges- 

 tion is due to acid! Noting, further, that saliva is acid to phenol- 

 thalein, suppose we infer that the amylolytic action of saliva is pri- 

 marily and directly due to acid secreted into the saliva! We should 

 then make — as did Fischer — a deduction in accord with some anal- 

 ogous and coincidental experimental findings, but which would not 

 follow from the premises. Would the observations on which our 

 deduction is based be sufficiently exclusive of other possible causa- 

 tive influences to Warrant the assumption that salivary digestion, 

 because of these analogies, is due wholly to acidic increase of the 

 affinities for water which are ordinarily shown by the "(hydrophilic) 

 emulsion colloids" under consideration — starches and dextrins? 

 We could not say, from actual knowledge, that such a conclusion 

 would be warrantfed by existing conditions. We have learned, of 

 course, that the amylolytic action of saliva is primarily and directly 

 due to the amylase in it and not to the acidity which saliva shows 

 toward phenolthalein, although the prevailing acidity may promote 

 the hydrating influence of the salivary amylase, without inducing by 

 itself any hydration that could be detected. We may even concede 

 that ptyalin itself is an acid without being forced to conclude that 

 acid, as we ordinarily conceive it, is the primary and direct causa- 

 tive agent in the hydrophilia and hydrolysis observed in the salivary 

 digestion of starch. 



Fischer's theory is a very attractive one and has the great merit 

 of simplicity — two reasons for my hope that additional evidence 

 will prove it to be correct in every detail to the further credit of 

 its brilliant author and to the very great satisfaction of every bio- 

 logical chemist. 



