SALIVA. 199 



agreeable articles has already been mentioned. The experiments of Frerichs 

 on dogs with gastric fistulae, and the observations of Gardner on a patient 

 with a wound in the oesophagus, have demonstrated that the flow of saliva 

 may be excited by the stimulus of food introduced directly into the stomach 

 without passing through the mouth. 



Quantity of Saliva. It is not easy to estimate in the human subject 

 the entire quantity of saliva secreted in the twenty-four hours ; and great 

 variations in this regard undoubtedly exist in different persons and even in the 

 same individual at different times. An approximate estimate may be arrived 

 at by noting as nearly as possible the average quantity secreted during the 

 intervals of digestion and adding to it the quantity absorbed by the various 

 articles of food. Estimates of this kind can be approximate only, and those 

 made by Dalton are apparently the most satisfactory. The following repre- 

 sents, according to Dalton, the quantities of saliva secreted during mastica- 

 tion and during the intervals of meals : 



Saliva required for mastication ^ 17-32 oz. (491 grammes). 



Saliva secreted in intervals of meals 27'93 oz. (792 grammes). 



Total quantity per day 45-25 oz. (1,283 grammes). 



The total daily quantity of saliva, therefore, is a little more than two and 

 three-fourths pounds. 



Eemembering that the quantity of saliva must necessarily be subject to 

 great variations, this estimate may be taken as giving a sufficiently close ap- 

 proximation of the quantity of saliva ordinarily secreted. It must be borne 

 in mind, however, with reference to this and the other digestive secretions, 

 that this large 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 dis- 

 charged from the organism. 



General Properties and Composition of the 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 

 discharged. . If it be allowed to stand, it deposits a whitish sediment, com- 

 posed mainly of desquamated epithelial scales with a few leucocytes, leaving 

 the supernatant fluid tolerably clear. Its specific gravity is variable, ranging 

 between 1004 or 1006 and 1008. Its reaction is almost constantly alkaline ; 

 although, under certain abnormal conditions of the system, it has occasion- 

 ally been observed to be neutral, and sometimes, though rarely, acid. The 

 saliva becomes slightly opalescent by boiling or on the addition of strong 

 acids. The addition of absolute alcohol produces an abundant, whitish, floc- 

 culent precipitate. Almost invariably the mixed saliva presents a more or 

 less intense blood -red tint on the addition of a per-salt of iron, which is due 

 to the presence of a sulphocyanide either of potassium or of sodium. 



A number of analyses of the human mixed saliva have been made by dif- 

 ferent chemists, presenting, however, few differences, except in the relative 

 proportions of water and solid ingredients, which are probably quite variable. 

 The following is an analysis by Bidder and Schmidt : 



