1/4 DIGESTION 



the relative proportions of water and solid ingredients, which probably 

 are quite variable. 



COMPOSITION OF HUMAN SALIVA 



Water .... .' . . . . . . . 995-J6 



Epithelium . . . : '. ' , ' . . ^ '" . . 1.62 



Ptyalin /'...-.. . ; * : ". >, ' .-r^ ." . ... 1.34 



Potassium sulphocyanate . .... .-...V * ... % . -.. 0.06 



Sodium, calcium and magnesium phosphates . - .- ' : i. ' ... 0.98 



Potassium chloride ) 



~. ,. i , , I 0.84 



Sodium chloride ) _. 



1000.00 



The organic matter of the mixed saliva, called ptyalin, on the addi- 

 tion of an excess of absolute alcohol, is coagulated in the form of whit- 

 ish flakes, which may readily be separated by nitration. This is the 

 substance described by Mialhe under the name of animal diastase. It 

 has no direct influence on nitrogenous alimentary matters, but when 

 brought in contact with hydrated or soluble starch, readily transforms 

 it, first into dextrin and afterward into maltose. The energy of this 

 action is such that one part is sufficient to effect the transformation of 

 more than two thousand parts of starch. 



The presence of a certain quantity of potassium sulphocyanate in 

 the mixed saliva can be demonstrated by the addition of a per-salt of 

 iron. This is a nearly constant and a normal ingredient of the human 

 saliva. 



Very little need be said concerning the other inorganic constituents 

 of saliva, except that they are of such a nature as almost invariably to 

 give a distinctly alkaline reaction. They exist in small proportion and 

 do not appear to be connected in any way with the action of the saliva 

 as a digestive secretion. 



USES OF THE SALIVA 



In 1831, Leuchs observed that hydrated starch, mixed with fresh 

 saliva and warmed, was converted into sugar. This fact has since been 

 repeatedly confirmed ; and it is now a matter of common observation 

 that boiled starch taken into the mouth almost instantly loses the prop- 

 erty of striking a blue color with iodin and responds to the copper- 

 tests for sugar. Of the rapidity of this action one can easily convince 

 himself by the simple experiment of taking a little boiled starch into 

 the mouth, mixing it well with the saliva, and testing in the ordinary 

 way. This can hardly be done so rapidly that the reaction does not 

 appear, and the presence of sugar is also indicated by the taste. Al- 

 though human mixed saliva will finally exert the same action on uncooked 

 starch, the transformation takes place much more slowly. 



