14 SALIVA. 



The observations of Mitscherlich on the parotid saliva of a 

 man suffering from chronic disease, show that prolonged hunger 

 or the use of indigestible and stimulating food, causes the secre- 

 tion of a concentrated saliva. Moreover, this observer found 

 that in the fasting state it was always acid, and that it was only 

 alkaline during meals. Magendie and Rayer perceived a gradual 

 diminution in the specific gravity of the parotid saliva of a 

 horse in whose Stenonian ducts fistulous openings had been 

 established. 



In regard to the chemical constituents of the parotid saliva, it 

 may be observed that the results of those who have experimented 

 on the subject, do not altogether coincide, probably from their 

 having operated on the saliva of different classes of animals. The 

 following may, however, be regarded as constant ingredients of 

 this secretion : 



(a) Potash, soda, and lime, combined with an organic matter: 

 this compound is one of the most important of the constituents 

 of the saliva, being that on which several of the properties of 

 this fluid are dependent; it is similar to, but not identical with, 

 albuminate of soda, and corresponds in part to the ptyalin of 

 Berzelius and others. 



Magendie, Jacubowitsch, and others, assume that alkaline car- 

 bonates are present in the saliva, but their quantity must be 

 extremely small in the fresh secretion ; the alkaline carbonates are 

 produced during the different steps of the chemical analysis, by 

 the access of atmospheric air. The formation of carbonate of lime 

 is extremely evident when the parotid secretion of the horse is 

 exposed to the air, for, like lime-water, it attracts carbonic acid, 

 and most beautiful microscopic crystals of carbonate of lime are 

 deposited. The organic matter, the ptyalin, is difficult of solu- 

 tion, although not absolutely insoluble, in water, after its sepa- 

 ration from the alkalies or from lime, by carbonic or some other 

 acid ; hence human saliva, and that of the dog, is sometimes 

 rendered turbid, and is sometimes apparently unaffected by 

 acids; the precipitate consists of amorphous flocculi, which are 

 difficult of solution in pure water, but dissolve readily if an alkali 

 or an acid be added. We find this substance in part still com- 

 bined with an alkali, both in the aqueous and in the spirituous 

 extracts ; it may be obtained in the greatest purity from the latter, 

 after extraction with alcohol and ether. It then forms an almost 

 gelatinous, colourless substance, which is more or less insoluble in 

 water, according as the alkali has been more or less thoroughly 



