12 SALIVA. 



The extreme variability of the specific gravity of the saliva of 

 even the same person, under different physiological relations, may 

 be easily demonstrated by a few experiments. I made some 

 experiments in reference to this point with the parotid secretion 

 of a horse, in whom an artificial salivary fistula was established, by 

 exposing and opening the duct of Steno. Very shortly after the 

 operation the parotid saliva had a density of 1*0061 ; ten minutes 

 afterwards, when the animal had drank about six pounds of water, 

 and had eaten some hay, the density sank to 1*0051 ; after having 

 nothing to drink for twelve hours, a feed of hay caused a free 

 secretion of saliva, whose specific gravity was as high as 1*0074. 

 Wright has pointed out that human saliva is denser after food 

 has been taken than in a fasting condition. He found that the 

 saliva of a healthy man who had lived for a week on a mixed diet, 

 varied in its density from 1*0079 to 1*0085 ; while, after a purely 

 animal diet for an equal time, it varied from 1*0098 to 1*0176; 

 and, after a purely vegetable diet, from 1*0039 to 1*0047. Ac- 

 cording to this author, moral emotions, atmospheric changes, light, 

 sound, &c., exert an influence on the density of the saliva. From 

 numerous experiments made on 200 healthy persons, he found 

 that the specific gravity of the saliva varied between 1*0089 and 

 1*0069, a result which is far higher than I have obtained from my 

 experiments. It is possible that the more abundant use of an 

 animal diet amongst the English may have caused the higher 

 density which was found by Wright. 



In relation to the alkalinity of the saliva, any one may readily 

 observe for himself that, during and after eating, the alkaline reac- 

 tion increases, while during fasting it very much diminishes, or 

 altogether disappears; indeed, in some persons who are apparently 

 healthy, the saliva during fasting has a weak acid reaction, although 

 immediately after the use of solid food it again becomes alkaline. 

 (Hunefeld*, Mitscherlichf, Wright, Jacubowitsch.) According 

 to Wright, the quantity of soda in the saliva of healthy men varies 

 between 0-095 and 0*353; in that of dogs between 0*151 and 

 0*653; in that of sheep between 0'087 and 0'261; and in that of 

 horses between 0*098 and 0*5 13. We only record these numbers 

 in order to give an approximate measure of the quantity of acid 

 which may be saturated by the saliva ; for these numbers are cal- 

 culated for soda, while in the saliva of graminivorous animals there 

 is often much potash, and always a large quantity of lime which is 

 * Chemie und Medicin. Berlin, 1841, S. 4360. 

 t Fogg. Ann. Bd. 27, S. 320347. 



