SALIVA AND GASTRIC JUICE. 251 



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

 into the opening of the Stenonian duct, and submaxillary saliva, or rather a 

 mixture of submaxillary and sublingual saliva, by similar catheterization of the 

 Whartonian duct. In animals the duct may be dissected out and a canula 

 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, possibly by the formation of an 

 excess of carbonic acid. On standing the clear fluid becomes turbid from a 

 precipitate of calcic carbonate, due to an escape of carbonic acid. It con- 

 tains 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 mucin more viscid ; 

 it contains salivary corpuscles, that is bodies closely resembling if not iden- 

 tical with leucocytes, and, often in abundance, amorphous masses. The so- 

 called chorda saliva in the dog, that is to say, saliva obtained by stimulating 

 the chorda tympani nerve (of which we shall presently speak), is under 

 ordinary circumstances thinner and less viscid, contains less mucin and 

 fewer structural elements than the so-called sympathetic 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 salts (in the dog 

 about 1 per cent.) than 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 submaxillary saliva being in most 

 cases more active than the parotid. In the rabbit, while the submaxillary 

 saliva has scarcely any action, that of the parotid is energetic. The saliva 

 of the cat is much less active than the above ; that of the dog is still less 

 active, indeed is almost inert. In the horse, sheep, and ox, the amolytic 

 powers of either mixed saliva or of any one of the constituent juices are 

 extremely feeble. 



Where the saliva of any gland is active, an aqueous infusion of the same 

 gland is also active. The importance and bearing of this statement will be 

 seen later on. From the aqueous infusion of the gland, as from saliva itself, 

 the ferment may be approximately isolated. In some cases at least some 

 ferment may be extracted from the gland even when the secretion is itself 

 inactive. In fact, a ready method of preparing a highly amylolytic liquid 

 tolerably free from proteid and other impurities is to mince finely a gland 

 known to have an active secretion, such, for instance, as that of a rat, to 

 dehydrate it by allowing it to stand under absolute alcohol for some days, 

 and then, having poured off most of the alcohol and removed the remainder 

 by evaporation at a low temperature, to cover the pieces of gland with strong 

 glycerin. Though some of the ferment appears to be destroyed by the 

 alcohol, a mere drop of such a glycerin extract rapidly converts starch 

 into sugar. 



Gastric Juice. 



187. There is no difficulty in obtaining what may be fairly considered 

 as a normal saliva ; but there are many obstacles in the way of determining 

 the normal characters of the secretion of the stomach. When no food is 



