RELATION OF THE SALIVARY GLANDS AND KIDNEYS. 47 



accomplishes a secondary object by its power of retaining gasefe in its 

 froth or foam. Atmospheric oxygen by this means is incor- Saliva carr i es 

 porated with the food during mastication, and is thus enabled air into the 

 to exert an important influence in promoting the action of 

 the gastric juice. For to the inception of the change which that juice 

 impresses on the food, oxygen is necessary. It is brought into the cav- 

 ity of the stomach entangled or dissolved in the saliva. 



It has just been mentioned that the action of saliva on starch is not re- 

 stricted to the production of sugar, but that it may end in the Lactic acid 



formation of lactic acid. If, therefore, any thing intervenes to 



check the supply of hydrochloric acid, which usually gives drochioric. 

 acidity to the gastric juice, the system possesses vathin itself the means 

 of compensating for the difficulty.. In the interior of the digesting mass 

 lactic acid is being set free. This acid, as has long been known, can re- 

 place hydrochloric acid in its physiological duty. 



Though so large a quantity of saliva as 20 ounces may be secreted in 

 a day, this being about one half of the urinary discharge, it is to be re- 

 membered that the water is not lost to the system, as in the latter case. 

 When the impure habit of profuse spitting is indulged in, it D isgusting e f_ 

 is interesting to remark the reflected effect which takes place feet of profuse 

 in the reduced quantity of the urine, and an instinctive desire 

 for water, a kind of perpetual thirst. It is probable that, under these dis- 

 gusting circumstances, the percentage amount of saline substances in the 

 saliva is increased, and that, so far as that class of bodies is concerned, 

 the salivary glands act vicariously for the kidneys, and the mouth is thus 

 partially converted into a urinary aqueduct. 



The relation between the salivary glands and the kidneys is very well 

 shown after the administration of such substances as the Relation of the 

 iodide of potassium. If five grains of this salt be taken in and^hlkid" S 

 pills, and the mouth be then thoroughly washed, in the course neys. 

 of a quarter of an hour the saliva will readily strike a blue tint when 

 tested with nitric acid and starch, but the urine will not show that reac- 

 tion until after a considerable interval, perhaps even an hour or more. It 

 w.ould therefore appear that such a salt must pass again and again through 

 the salivary glands before it is finally disposed of by the kidneys, which 

 oifer the only outlet for its total removal. 



Among the functions of the saliva we ought not to overlook the influ- 

 ence which its rapid secretion must exert on the state of tension of the 

 blood-vessels, an influence which probably favors the absorption going on 

 in the stomach and intestines. 



Thus prepared by mastication and in,salivation, the food descends into 

 the stomach, passing along the pharynx, which dilates to receive it. The 

 rima glottidis spontaneously closes, and additional security is given to the 



