272 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



The salts consist mainly of phosphates of sodium, potassium and 

 magnesium, and alkaline chlorides. One of the most remarkable con- 

 stituents of the saliva is the sulphocyanide of potassium which is found 

 in small amounts in many but not in all salivary secretions. Treviranus 

 in 1814 first made the observation that when saliva is mixed with a solu- 

 tion of oxide or chloride of iron and hydrochloric acid a bright-red 

 coloration is produced, which was recognized by Gmelin to depend upon 

 the presence of the sulphocyanide of potassium. It is said by Gmelin 

 to be present in largest amount in the saliva of the dog ; it is almost con- 

 stantly present in the saliva of man and in the saliva of the horse. It 

 probably, however, may be detected in the saliva of all animals by dis- 

 tilling the saliva with phosphoric acid and catching the first drops that 

 pass over on filter-paper treated with dilute lrydrochloric acid and ferric 

 chloride, and then dried. Its presence may also be recognized by the 

 fact that paper, impregnated with tincture of guaiacum and then dried, 

 with an almost colorless solution of sulphate of copper, is colored blue 

 by the saliva. The reaction by which potassium sulphocyanide is recog- 

 nized — that is, the red color which it forms with an iron salt — is possessed 

 also by meconic acid ; the two substances may be distinguished, how- 

 ever, in a very simple manner. If a few drops of a solution of mercuric 

 chloride, or if a few mercuric chloride crystals, are added to saliva which 

 has been colored red by the perchloride of iron, the color is at once dis- 

 charged. When, however, the red color is due to the presence of 

 meconic acid and an iron salt, the red coloration is permanent, even 

 after the addition of corrosive sublimate. 



The origin of this salt is not known, although the majority of 

 authorities seem to attribute its presence to a spontaneous decompo- 

 sition of the saliva, since saliva which has been standing for some time 

 will give the reaction in a more marked degree than when entirely fresh. 

 This view is still further strengthened by the fact, determined by Ellen- 

 berger and Hofmeister, that extracts of the salivary glands of all the 

 domestic animals, whether made from dried or fresh glands, with water, 

 carbolized or alkaline water or glycerin, entirely fail to show this re- 

 action. Absolute data as to the origin of this salt are entirely wanting. 

 Its use in the economy is also clouded in obscurity, as it is eliminated 

 unchanged through the kidneys and may be recognized in the urine. 

 The chlorides in saliva may be recognized by filtering and acidulating 

 strongly with nitric acid; the addition then of a few drops of a solution 

 of nitrate of silver to the saliva will cause quite a decided white precipi- 

 tate which is readily soluble in ammonia. 



Of organic constituents, saliva contains albuminous bodies, as may 

 be recognized by the xanthoproteic and Millon's reaction; it contains 

 mucin, as may be determined by precipitating with acetic acid; and it 



