BY I)R. LADDER BRUNTON. 463 



hours. Then, having poured off the liquid, squeeze the re- 

 mainder in a cloth, so as to get rid of as much of the alcoholic 

 extract as possible. The cake so obtained must now be mixed 

 with as much glycerin as will cover it in a beaker, and allowed 

 to remain for several days, during which the mixture may be 

 occasional^ stirred. At the end of this period, the whole 

 must be strained through muslin, and then filtered through 

 paper. In the filtrate, ptyalin is precipitated by the addition 

 of alcohol in excess. The precipitate, after having been col- 

 lected by subsidence and decantation, must be dried over sul- 

 phuric acid. 



83. Separation of Ptyalin from Saliva. The method 

 employed for separating ptyalin as well as other ferments from 

 the secretions in which they are contained, depends on the fact 

 that when a copious precipitate is produced in the fluid, the fer- 

 ment adheres to the particles of the precipitate, and is carried 

 down along with them. It does not, however, adhere very 

 closely to the precipitate, and can readily be washed off. The 

 precipitate employed to carry down ptyalin is calcium phos- 

 phate. This carries down with it not only the ptyalin, but 

 also the albumin in the saliva. The albumin, however, adheres 

 more closely than the ptyalin to the precipitate, so that the 

 ptj'alin is dissolved away by the first wash -water, while the 

 albumin remains adherent. Collect a considerable quantity of 

 saliva by filling the mouth with ether; while fresh, acidify it 

 strongly with phosphoric acid, so that the precipitate to be pro- 

 duced may be voluminous; then add milk of lime till the fluid 

 has a faintly alkaline reaction, and filter. When the fluid has 

 drained from the precipitate, remove the latter into a fresh 

 beaker, add to it a little water, not exceeding in amount the 

 saliva originally employed, stir it veil and filter again. Add 

 to the filtrate an excess of alcohol. After some time a fine 

 white flocculent precipitate will separate, which must be col- 

 lected in a filter and dried over sulphuric acid. It then forms 

 a snow-white powder, and consists of ptyalin mixed with some 

 inorganic salts. To obtain it free from ash, dissolve it in water, 

 and precipitate it again by absolute alcohol. Pour off the alco- 

 hol, dissolve again in water, and precipitate again. Repeat this 

 several times, collect the precipitate on a filter, wash with dilute 

 alcohol, and then with a little water, and finally dry it at a low 

 temperature, under a bell-jar over sulphuric acid. 



* 84. Properties of Ptyalin. The reactions of ptyalin 

 may be examined either in the filtered aqueous solution of the 

 calcium phosphate precipitate, or in solutions of pure pt3 r alin. 

 Ptyalin differs entirely from albumin in its reactions. 



1. Add nitric acid; there is no precipitate. Boil the liquid, 

 allow il~ to cool, and add ammonia. No yellow color is produced. 



2. Add to several portions in test-tubes, mercuric chloride; 



