^ 



DIGESTION. \s 



^^texTTA* 



COMPOSITION OF THE SALIVA. ^-4* 1 A- 



Water 995.16 



Albuminous matter . 1.34 



Potassium Sulphocyanide ...... 0.06 



Calcareous, magnesian, and alkaline phosphates . . 0.98 



Sodium and Potassium chlorides . . . . , , . 0.84 



Mixture of epithelium ...... 1.62 



1000.00 



Saliva, accordingly, is one of the least concentrated of the digestive 

 secretions, containing but a small quantity of organic matter, and by 

 no means a large proportion of mineral salts; its watery ingredient 

 being by far the most abundant, as compared with the other animal 

 fluids. Its albuminous matter consists of a small quantity of albumen, 

 coagulable by heat or a mineral acid ; more or less mucine, which gives 

 to it a slightly viscid character, and is coagulable by acetic acid ; and 

 pty aline, a substance belonging to the class of ferments, which is 

 thrown down by alcohol in excess. Some of these reagents, accord- 

 ingly, precipitate all the albuminous matters present, while others coag- 

 ulate only a part of them. The sulphocyanide may be detected by 

 adding to the saliva a small quantity of a solution of iron chloride, 

 when the characteristic red color of iron sulphocyanide is produced. 

 A similar red color is produced by the action of the ferric salts upon 

 meconic acid, or the meconates ; but the two may be distinguished 

 from each other by the fact that the red color caused by the presence 

 of a sulphocyanide is destroyed by the addition of either gold chloride 

 or mercurial bichloride, neither of which affects that produced by 

 meconic acid. The presence of a sulphocyanide in human saliva is 

 almost constant, and we have never failed to find it., in the freshly 

 collected secretion. Tierordt has calculated its amount in saliva by 

 measuring the absorption of light in the green and blue portions of 

 the spectrum of the red fluid produced on the addition of iron chloride ; 

 and has found it, in an average of six observations, to be 0.16 parts 

 per thousand. 



Saliva, like various other animal fluids, has the property of con- 

 verting boiled starch into glucose at the temperature of 38 C. Its 

 action is not strictly confined to this temperature, but will go on, 

 though with diminished rapidity, both above and below it, if the vari- 

 ation be not too great. It is suspended, however, at or near the 

 freezing-point, and is permanently arrested by boiling water. It 

 depends on the presence of ptyaline, the special ferment of the saliva, 

 which, like other similar bodies, is most active at or near the temper- 

 ature of the living body. It is differently affected, however, by cold 

 and heat. By a freezing temperature its action is suspended for the 

 time, but recommences when warmth is again applied ; while boiling 

 permanently destroys its catalytic property. 



The secretions produced by the different salivary glands vary in their 

 physical properties, especially in the degree of their viscidity. 



