170 DIGESTION. 



be subject to great variations, this estimate may be taken as 

 giving a sufficiently close approximation of the quantity of 

 saliva ordinarily secreted. It must be borne in mind, how- 

 ever, with reference to this and the other digestive secretions, 

 that this immense quantity of fluid is at no one time removed 

 from the blood, but is reabsorbed nearly as fast as secreted, and 

 that normally, none of it is discharged from the organism. 



General Properties and Composition of Saliva. The 

 mixed fluid taken from the mouth is colorless, somewhat 

 opaline, frothy, and slightly viscid. It generally has a faint 

 and somewhat disagreeable odor very soon after it is dis- 

 charged. If it be allowed to stand, it deposits a . whitish 

 sediment composed mainly of desquamated epithelial scales, 

 with a few leucocytes ; leaving the supernatant fluid tolera- 

 bly clear. Its specific gravity is variable ; ranging from 

 1,004 to 1,006 or 1,008. Its reaction is almost constantly 

 alkaline ; though, under certain abnormal conditions of the 

 system, it has occasionally been observed to be neutral, and 

 sometimes, though rarely, acid. We have occasionally ob- 

 served a distinctly acid taste in the saliva after very se- 

 vere, prolonged, and exhaustive muscular exertion. The sa- 

 liva becomes slightly opalescent by boiling and on the addi- 

 tion of the strong acids. The addition of absolute alcohol 

 produces an abundant, whitish, flocculent precipitate. Al- 

 most invariably the mixed saliva presents a more or less in- 

 tense blood-red tint on the addition of a per-salt of iron, 

 which is due to the presence of a sulpho-cyanide, either of 

 potassium or sodium. 



A number of analyses of the human mixed saliva have 

 been made by different chemists, presenting, however, few 

 differences, except in the relative proportions of water and 

 solid ingredients, which are probably quite variable. One 

 of the most recent of these analyses is the following by Bid- 

 der and Schmidt : 1 



1 BIDDER UND SCHMIDT, Die Verdauungssafte, Leipsig, 1852, S. 11. 



