64 PHYSIOLOGY OF ALIMENTATION. 



The mucous glands of the mouth secrete a small amount of 

 an exceedingly tenacious material containing much mucin. 

 This secretion has never been obtained pure in the human 

 being, but experimentally it has been gotten from dogs after 

 ligature of the ducts or extirpation of the entire set of salivary 

 glands. The secretion is mixed with many epithelial cells 

 from the mouth. 



The mixed saliva is that usually employed for experimental 

 purposes. The amount of this secretion in twenty-four hours 

 is stated by BIDDER and SCHMIDT l to be 300 to 1500 c.c. The 

 quantity secreted in the unit of time is largest during meals 

 and falls to a minimum between meals. These variations will 

 be discussed in greater detail later. The mixed saliva froths 

 easily and is somewhat turbid, from admixture with epithelial 

 cells and some leucocytes, together with the mucin obtained 

 chiefly from the mucous glands of the mouth. The saliva 

 contains vast numbers of bacteria. 2 The average specific 

 gravity is 1.003 to 1.004. The reaction is ordinarily stated 

 to be alkaline, but recent observations seem to indicate 

 that it is neutral, perhaps even acid, in reaction. That saliva 

 is able to neutralize strong acids does not indicate that this 

 secretion is alkaline in reaction, but simply that it contains 

 salts of strong bases combined with weak acids, such as car- 

 bonates and bicarbonates. 



Toward litmus, lacmoid, and rosolic acid saliva reacts as 

 though it were alkaline. When phenolphthalein is used, how- 

 ever, the solution remains colorless. Ten cubic centimeters of 

 mixed saliva require 0.2 c.c. of a 1/10 normal alkali solution 

 before the phenolphthalein will just turn pink, indicating an 

 alkaline reaction. Saliva is therefore to be considered as at 

 least neutral, if anything else, slightly acid, for phenolphthalein 

 is in this case to be looked upon as a more reliable indicator 

 than any of the others mentioned above. What holds for the 



1 VIERORDT: Tabellen, Jena, 1888, p. 128. 



2 See p. 160. 



