138 



MANUAL OF PHYSIOLOGY. 



FIG. 63. 



can be drawn into threads. The amount secreted by an adult 

 human being during twenty-four hours varies greatly according 

 to circumstances, and has been variously estimated by different 

 authors, by whom the wide limits of 200-2000 grms. (7-70 oz.) 

 have been assigned as the daily amount. 



The saliva contains about 0.5 per cent, of solids. Of these the 

 greater part are organic, namely : (1) Mucin, from the sub-max- 

 illary, sublingual, and small mucous glands, which can be pre- 

 cipitated by acetic acid. To this 

 substance the viscidity of the 

 saliva is due. (2) Traces of al- 

 bumin precipitable by concen- 

 trated nitric acid and boiling. 

 (3) Traces of globulin, precipi- 

 tated by carbonic acid. (4) 

 Ptyalin, a peculiar ferment. 



The inorganic constituents are 

 salts, among which an inconstant 

 amount of potassium sulpho-cya- 

 nate is found, a substance which 

 does not exist in the blood. 



There are also many morpho- 

 logical elements : of these the majority are accidental, being the 

 remains of food, etc. ; others are more or less characteristic, 

 namely : (1) Salivary corpuscles which are rounded protoplas- 

 mic masses containing nuclei and coarse granules which show 

 Brownian movements. (2) Epithelial scales from the surface of 

 the mucous membrane of the mouth. (3) Various forms of pro- 

 tophyta, which propagate readily amid the decaying particles of 

 food in the mouth. But no bacteria or other fungi exists in the 

 ducts of the glands or saliva taken from the ducts with the 

 necessary aseptic precautions. 



The ordinary mixed saliva* may be easily collected by chewing 

 some insoluble material, such as a bit of rubber tubing, and col- 

 lecting the fluid which the motion causes to be poured into the 

 mouth. 



The collection of the secretion of the different glands requires 



The form elements from mixed saliva 

 from tip of tongue, showing (e) large ir- 

 regular scaly epithelial cells, (c) round 

 salivary corpuscles, several (6) bacteria, 

 and (TO) micrococci. 



