34 SALIVA. ' 



observed its action on starch. These facts cannot, however, be 

 placed in comparison with the action of the mixed saliva, which 

 does not require any long exposure to the' atmosphere in order to 

 acquire this property, and is only exceeded in this power by the 

 diastase of germinating seeds and by the pancreatic juice. 



Another point which must appear doubtful to those who have 



not experimented for themselves, is the question whether acid 



saliva has the same saccharifying force as the alkaline secretion 



a view most positively denied by Sebastian, Wright, and Bernard; 



and as confidently asserted by Jacubowitsch and Frerichs. In my 



former experiments I failed, like the first-named observers, in 



effecting the conversion of starch by saliva, and notwithstanding 



the most careful inquiry, I have been unable to detect the causes 



of that failure ; but in my more recent experiments, when I have 



allowed saliva treated with acetic, sulphuric, hydrochloric, or nitric 



acid, to act on either crude or boiled starch, I have always observed 



a tolerably rapid formation of sugar, and have convinced myself 



that acids can no more impede the digestive power of the saliva 



than alkalies can promote it. It is therefore certain that mixed 



saliva, whether it be alkaline or acid, acts on starch with equal 



energy at equal temperatures. Trommels sugar-test cannot be 



directly applied in this investigation, for Frerichs has shown by 



an interesting experiment that suboxide of copper is immediately 



separated when saliva and starch are boiled with potash and 



sulphate of copper; we must, therefore, remove any starch or 



dextrin that may remain in the filtered fluid, by treating it with 



alcohol, before applying Trommer's test, or we must adopt some 



other means of demonstrating the presence of sugar in the mixture. 



The albuminous substance occurring in the saliva, to which 



Mialhe has given the name of Diastase salivaire, is undoubtedly 



similar in many respects to diastase; but, on a rigid examination, 



the two substances are found to be altogether different. Mialhe 



obtains this salivary diastase by precipitating human saliva with 



absolute alcohol. On referring to the composition of saliva, it is 



easy to perceive that the substances which will be precipitated by 



alcohol are chiefly ptyalin and mucus with a quantity of salts, and 



it is in the mixture of these substances that Mialhe thinks that he 



has found the active principle of the saliva. In experiments with 



this mixture, I have altogether failed in obtaining evidence of the 



extraordinary powers which were attributed to it by Mialhe (who 



maintains that 1 part can rapidly effect the metamorphosis of 8000 



parts of starch at a temperature of 37); and although I formerly 



