238 SALIVA. [BOOK n. 



Mixed saliva, whose properties we have just discussed, is the 

 result of the mingling in various proportions of saliva from the 

 parotid, submaxillary, and sublingual glands with the secretion 

 from the buccal glands. These constituent juices have their own 

 special characters, and these are not the same in all animals. 

 Moreover in the same individual the secretion differs in composition 

 and properties according to circumstances ; thus, as we shall see in 

 detail hereafter, the saliva from the submaxillary gland secreted 

 under the influence of the chorda tympani nerve is very different 

 from that which is obtained from the same gland by stimulating 

 the sympathetic nerve. 



In man pure parotid saliva may easily be obtained by introducing a 

 fine cannula into the opening of the Stenonian duct, and submaxillary 

 saliva, or rather a mixture of submaxillary and sublingual saliva, by 

 similar catheterisation of the Whartonian duct. In animals the duct 

 may be dissected out and a cannula introduced. 



Parotid saliva in man is clear and limpid, not viscid ; the reaction 

 of the first drops secreted is often acid, the succeeding portions, 

 at all events when the flow is at all copious, are alkaline ; that is 

 to say the natural secretion is alkaline, but this may be obscured 

 by acid changes taking place in the fluid which has been retained 

 in the duct. On standing, it becomes turbid from a precipitate of 

 calcic carbonate, due to an escape of carbonic acid. It contains 

 globulin and some other forms of albumin, with little or no mucin. 

 Potassium sulphocyanate may also sometimes be detected, but 

 structural elements are absent. 



Submaxillary saliva, in man and in most animals, differs from 

 parotid saliva in being more alkaline and, from the presence of 

 mucus, more viscid; it contains, often in abundance, salivary 

 corpuscles, and amorphous masses of proteid material. The so- 

 called chorda saliva in the dog, of which we shall presently speak, is 

 under ordinary circumstances thinner and less viscid, contains less 

 mucus, and fewer structural elements, than the so-called sympa- 

 thetic saliva, which is remarkable for its viscidity, its structural 

 elements, and for its larger total of solids. 



Sublingual saliva is more viscid, and contains more mucin and 

 more total solids (in the dog 275 p. c.), than even the submaxillary 

 saliva. 



The action of saliva varies in intensity in different animals. 

 Thus in man, the pig, the guinea-pig, and the rat, both parotid 

 and submaxillary and mixed saliva are amylolytic; the sub- 

 known example. The fermentative activity of yeast which leads to the conversion 

 of sugar into alcohol, is dependent on the life of the yeast-cell. Unless the yeast- 

 cell be living and functional, fermentation does not take place; when the yeast- 

 cell dies fermentation ceases ; and no substance obtained from yeast, by precipita- 

 tion with alcohol or otherwise, will give rise to alcoholic fermentation. The salivary 

 ferment belongs to the latter class; it is a substance, not a living organism 

 like yeast. 



