142 DIGESTION. 



tated both by a boiling temperature and by alcohol in excess. Some 

 of these reagents, accordingly, precipitate all the albuminous matters 

 of the saliva, while others produce coagulation of only a part of them. 

 The sodium sulphocyanide of the saliva may be detected by adding to 

 the secretion a small quantity of a solution of iron chloride, when the 

 characteristic red color of iron sulphocyanide is produced. A similar 

 red .color is also produced by the action of the ferric salts upon 

 me conic acid, or the meconates ; but the two substances may be dis- 

 tinguished 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 the tint pro- 

 duced by meconic acid. The presence of a combination of sulphocy- 

 anogen in human saliva is almost constant, and we have never failed to 

 find it in the freshly collected secretion by the iron-chloride test. 

 Yierordt 1 has calculated the amount of potassium sulphocyanide in 

 saliva by measuring the absorption of light in the green and blue por- 

 tions 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. 



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

 verting hydrated starch into glucose if mingled with it at or about a 

 temperature of 38 (100 F.). The change is not confined to precisely 

 this temperature, but will go on, with diminished rapidity, both above 

 and below it, if the degree of cold or warmth be not too great. It is 

 entirely suspended, however, at or near the freezing point, and is per- 

 manently arrested by the temperature of boiling water. It depends, in 

 the saliva, upon the presence of pty aline, which acts in this respect like 

 the "diastase" of certain vegetable substances. Like other similar 

 matters which exert a so-called " catalytic" action, it will produce its 

 effect only within certain limits of temperature, and is most efficient at 

 about the warmth of the living body. It is affected differently, how- 

 ever, by the action of cold and that of heat ; for while a freezing tem- 

 perature only suspends it for the time being, and allows it to recommence 

 when moderate warmth is again applied, a boiling temperature at once 

 coagulates the pty aline and destroys its catalytic property. Saliva, 

 therefore, which has been boiled for a few instants and allowed to cool, 

 is found to have permanently lost its power of transforming starch 

 into sugar. 



This action of human saliva on hj^d rated starch takes place sometimes 

 with great rapidity. Traces of glucose may often be detected in the 

 mixture in one minute after the two substances have been brought in 

 contact ; and we have even found that starch paste, introduced into the 

 cavity of the mouth, if already at the temperature of 38, will yield 

 traces of sugar at the end of half a minute. The rapidity, however, with 



1 Anwendung des Spectralapparates zur Photometric der Absorptionsspectren. 

 Tubingen, 1873, p. 147. 



