918 THE EXTERNAL SECRETIONS 



bloodless gland is able to secrete saliva, but since this organ is unable 

 to acquire new material, the secretion will be scanty in amount. 



The General Character of Saliva. — When collected directly from 

 the mouth, saliva is a transparent, slightly opalescent and slimy 

 liquid, possessing a moderate viscosity and a specific gravity of 1.002 

 to 1.006.-^ On standing it becomes cloudy, this change being due to the 

 deposition of calcium carbonate in consequence of the escape of car- 

 bonic acid which formerly retained this salt in the form of its bicarbon- 

 ate. The reaction of saliva is slightly alkaline, but may become 

 moderately sour during the night and during fevers and digestive 

 disorders. The reason for this is the diminution in its quantity 

 which favors the bacterial decomposition of its organic constituents. 

 Its active principle, ptyalin, ceases to act in a markedly alkaline or 

 slightly acid medium; in fact, free hydrochloric acid in an amount 

 equalling a 0.003 per cent, solution suffices to stop its action entirely. 

 Temperatures of 0° C. and 65° to 70° C. have a similar effect. 



The quantity of saliva secreted in a day has been estimated in man at 1 to 2 

 liters, in horses at 40 liters, and in the large ruminating animals at 60 liters. It 

 contains 0.5 per cent, of solids, which may be classified as follows: 



Organic: Mucin, which gives to it its ropy, mucilaginous character. 

 Ptyalin, an amylolytic enzyme. 

 Protein, of the nature of a globulin. 

 Potassium sulphocyanide. 

 Inorganic: Sodium chlorid, sodium carbonate. 



Calcium phosphate and carbonate, magnesium phosphate and potas- 

 sium chlorid. 



Suspended in the saliva are desquamated epithelial cells, disintegrating leukocytes, 

 the so-called "salivary corpuscles," gland cells and clumps of mucin. Among the 

 living organisms might be mentioned a number of saprophytes, such as leptothrix 

 buccalis, and pathogenic bacteria. 



CHAPTER LXXIX 



THE DIGESTIVE SECRETIONS (CONTINUED) 



B. THE GASTRIC AND PANCREATIC SECRETIONS 



The Gastric Glands. — The cavity of the stomach is divided into 

 a cardiac, fundic and pyloric portion. It is lined throughout by a soft 

 and thick mucosa which presents a honeycomb appearance owing to 

 the presence of numerous shallow polygonal depressions. Its unusual 

 thickness is due very largely to the fact that it is made up of an almost 

 infinite number of closely packed, long tubular glands which are held 



1 Burton-Opitz, Biochem. Bull., 1919; Neilson and Terry, Am. Jour, of Physiol., 

 XV, 1906, 406; Tezas, Maly, xxv, 1905. 



