210 THE FLUIDS. 



Iodide of potassium is always found in saliva after the use of 

 iodine, and mercury enters it in case of mercurial salivation. It is 

 also acid in certain abnormal states, and usually so during fasting. 



Origin. Saliva is secreted by the epithelial cells of the minute 

 subdivisions of the ducts in the three salivary glands. 



Uses. The mechanical functions of saliva are fivefold : 



1. It conduces to phonation and articulation, by securing a proper 

 degree of moisture of the tongue and oral cavity. 



2. It aids the sense of taste. 



3. It cleanses the mucous membrane of the oral cavity. 



4. To a certain extent it quenches, or rather prevents, thirst. 



5. It aids in mastication and deglutition, and carries air into the 

 stomach, the latter being inclosed in the form of bubbles during 

 mastication. Bernard has shown, however, that it is the parotid 

 secretion which prevents thirst, while that of the sublingual is sub- 

 servient to deglutition, and that of the submaxillary conduces to 

 the perfection of taste. 



An important chemical agency has also been attributed to saliva; 

 the power of changing the starch of the food into sugar. Bernard 

 has, however, proved that only mixed saliva has this effect, and 

 only when in a state of incipient decomposition. In fact, the influence 

 of saliva upon starch has been much overrated ; the pancreatic and 

 intestinal fluids being the principal agents for the conversion of the 

 amylacea into sugar. It normally only hydrates the starch after it 

 arrives in the stomach. 



2. Bile. 



Bile, as obtained from the gall-bladder, is a viscid fluid, capable 

 of being drawn into threads; of a green or brown color, a bitter 

 taste, and a peculiar odor (often resembling musk). Its specific 

 gravity is about 1020, and it is usually alkaline, often neutral, and 

 very rarely acid, even in disease. When it contains much mucus, 

 it putrefies very readily; when nearly free from it, with difficulty, 

 or not at all. It doubtless always contains some of this element, 

 and to its presence the viscidity of the bile is due. Pure bile has 

 not yet been analyzed. 



The only morphological element in bile is the conoid al epithelial 

 cell of the gall-bladder and biliary ducts. 



Bile, as usually obtained for examination, contains, on the average, 

 14 per cent. (10.2 to 17.3) of solid constituents; 90 per cent, of these 



