44 PROPERTIES OF MIXED SALIVA. 



secretions of the various salivary glands. It may be doubted whether 

 Properties of the method of obtaining it sometimes recommended, by mak- 

 mixed salivas. j n g pressure under the chin and tickling the fauces with a 

 feather, yields it of normal constitution. It is described as an alkaline 

 juice, of a bluish color or colorless, in consistency glairy, readily froth- 

 ing, and therefore well adapted for entrapping atmospheric air. It con- 

 tains, of solid matter, from 0.348 to 0.841 per cent. Its alkali appears, 

 for the most part, to be combined with an organic substance, ptyaline, 

 from which it may be separated by the weakest acids, such as carbonic. 

 In the ash of saliva the alkali occurs chiefly as phosphate : this arises from 

 rearrangement of the constituents during incineration. The saliva con- 

 tains but a trace of alkaline sulphates, the chlorides of sodium and potas- 

 sium preponderating over all the other mineral ingredients. 



On standing, saliva separates into two layers : a transparent one, which 

 is supernatant, and a grayish turbid one below, which consists of a de- 

 posit of particles of pavement epithelium and mucus corpuscles, derived 

 from the lining membrane of the mouth and the salivary ducts. Its 

 chemical reaction varies to some extent with the state of the system ; thus, 

 after long-continued fasting, from being alkaline, it may approach the neu- 

 tral state. By some it is asserted that under these conditions it may 

 even become acid. There is no proof that this is owing to the appear- 

 ance of lactic acid : it may be due to butyric acid, or even the acid phos- 

 phate of soda. In morbid conditions this reaction is by no means infre- 

 quent : it has been commonly observed in intestinal inflammation, acute 

 rheumatism, intermittent fever. Donne and Frerichs assert that acidity 

 of the saliva depends on an irritation of the buccal mucous membrane. 



The specific gravity of mixed saliva varies from 1.004 to 1.009. These 

 variations depend on many different causes, there being a diminution after 

 the taking of drink, and a greater increase after taking food, than even is 

 observed in the fasting state. An animal diet especially increases it. 



Under ordinary circumstances, the saliva is secreted to an amount of 

 Quantity of from 15 to 20 ounces daily. The exudation is more copious 

 saliva. during mastication, speaking, reading, more being produced by 

 the use of hard than soft food. Mental emotions exert a control over its 

 flow, sometimes diminishing it, as in moments of anxiety, sometimes in- 

 creasing it, as by the anticipation of food. After eating, the flow contin- 

 ues to a considerable extent ; it is also provoked by the use of aromatics. 

 On irritation of the interior of the stomach through a gastric fistula, the 

 flow is simultaneous with that of the gastric juice. 



The movements of the jaw and the pressure of the food give rise to va- 

 riations in the quantity of saliva. It is perhaps for these, reasons that the 

 parotid gland on that side of the mouth which is most used in mastication 

 secretes more than the other. Of the proportion of the different kinds of 



