SALIVA. | 125 



of iron. The alkaline reaction of the saliva varies in intensity 

 during the day, but is nearly always sufficiently distinct. 



The saliva is not a simple secretion, but a mixture of four dis- 

 tinct fluids, which differ from each other in the source from which 

 they are derived, and in their physical and chemical properties. 

 These secretions are, in the human subject, first, that of the parotid 

 gland ; second, that of the submaxillary ; third, that of the sub- 

 lingual ; and fourth, that of the mucous follicles of the mouth. 

 These different fluids have been comparatively studied, in the 

 lower animals, by Bernard, Frerichs, and Bidder and Schmidt. 

 The parotid saliva is obtained in a state of purity from the dog by 

 exposing the duct of Steno where it crosses the masseter muscle, 

 and introducing into it, through an artificial opening, a fine silver 

 canula. The parotid saliva then runs directly from its external 

 orifice, without being mixed with that of the other salivary glands. 

 It is clear, limpid, and watery, without the slightest viscidity, and 

 has a faintly alkaline reaction. The submaxillary saliva is ob- 

 tained in a similar manner, by inserting a canula into Wharton's 

 duct. It differs from the parotid secretion, so far as its physical 

 properties are concerned, chiefly in possessing a well-marked vis- 

 cidity. It is alkaline in reaction. The sublingual saliva is also 

 alkaline, colorless, and transparent and possesses a greater degree 

 of viscidity than that from the submaxillary. The mucous secre- 

 tion of the follicles of the mouth, which forms properly a part of 

 the saliva, is obtained by placing a ligature simultaneously on 

 Wharton's and Steno's ducts, and on that of the sublingual gland, 

 so as to shut out from the mouth all the glandular salivary secre- 

 tions, and then collecting the fluid secreted by the buccal mucous 

 membrane. This fluid is very scanty, and much more viscid than 

 either of the other secretions ; so much so, that it cannot be poured 

 out in drops when received in a glass vessel, but adheres strongly 

 to the surface of the glass. 



We have obtained the parotid saliva of the human subject in a 

 state of purity by introducing directly into the orifice of Steno's 

 duct a silver canula ^5 to 2 V of an inch in diameter. The other 

 extremity of the canula projects from the mouth, between the lips, 

 and the saliva is collected as it runs from the open orifice. This 

 method gives results much more valuable than observations made 

 on salivary fistulas and the like, since the secretion is obtained 

 under perfectly healthy conditions, and unmixed with other animal 

 fluids. 



