ANIMAL AMIDES. 



The portion insoluble in boiling water is not dissolved by ace- 

 tic acid. It is partially dissolved in cold potash ley.* 



CHAPTER V. 



OF SALIVIN. 



SALIVIN or ptyalin, as it is also called, is a peculiar substance 

 which exists in human saliva. It seems to have been first no- 

 ticed by Dr Bostock in 1805, who describes it under the name 

 of pure mucusj It is not described by Berzelius in the second 

 volume of his Djurkemien, published in 1808. But in his paper 

 on the Chemical Properties of Animal Fluids, published in 1813, 

 it is particularly noticed under the name Salivary, or peculiar Ani- 

 mal Matter. \ More lately its properties have been examined by 

 Tiedemann and L. Gmelin. Salivin may be obtained in the 

 following manner : 



Evaporate saliva to dryness in a gentle heat. Digest the re- 

 sidual mass in rectified spirits, which dissolve most of the salts 

 of saliva. An additional portion of alcohol acidulated with ace- 

 tic acid will remove any soda that might still remain. Nothing 

 now remains but a mixture of salivin and mucus. Water dis- 

 solves the former of these substances, and leaves the mucus. The 

 aqueous solutions being evaporated in a gentle heat, leaves pure 

 salivin. 



Thus obtained it is a transparent white substance, which does 

 not crystallize, and is destitute of taste and smell. It is not al- 

 tered by exposure to the air. It dissolves readily in water, but 

 is insoluble in alcohol. The aqueous solution is not precipitat- 

 ed by alkalies or acids, nor by solutions of diacetate of lead, || 

 corrosive sublimate, or of tannin. It does not become turbid on 

 boiling, and does not gelatinize when the concentrated solution 

 is allowed to cool. The only substances which precipitate it from 

 its aqueous solution are alcohol and nitrate of silver. And this 



* Berzelius, Trait6 de Chimie, vii. 558. 



t Nicholson's Jour. ii. 251. \ Annals of Philosophy, (1st series,) ii. 380. 

 Recherches Experimen tales, i. 12. 



|| Bostock obtained a precipitate with this salt because his salivin contained 

 uncombined soda. 



