46 GASTRIC DIGESTION. 



times, and add a drop of it to one of the portions ; to another add a drop of 

 potash solution similarly diluted. Heat all three tubes gradually, and note 

 the temperature at which each coagulates. 



8. Make alkali-albumin solution as in 3. Divide it into two equal parts. 

 To one add two or three drops of ten per cent, ..solution of sodic phosphate. 

 Colour both with litmus and neutralize with weak acid. The portion without 

 sodic phosphate is precipitated. The other portion is not precipitated until 

 enough acid has been added to convert the sodic phosphate present into acid 

 sodic phosphate. 



IV. Characteristics of Proteids. Peptic Digestion. 



1. Tests for proteid bodies in solution. 



a. To some of the albuminous liquid referred to in iii, 2, add strong 

 nitric acid. The precipitate obtained turns yellow on boiling. 



b. Cool the liquid in a and add strong ammonia. The precipitate assumes 



an orange tint (Xanthoprotein reaction). 



c. To another portion add Millon's reagent. (Mercury is dissolved in 

 its own weight of strong nitric acid. The solution so obtained is diluted 

 with twice its volume of water. The decanted clear liquid is Millon's 

 reagent.) A precipitate is formed which turns dull red on boiling. 



d. To a third portion add solution of potassic ferrocyanide, and a drop of 

 acetic acid. A white precipitate appears. 



e. Introduce a fourth portion of the liquid into a test-tube containing one 

 drop of ten per cent, solution of cupric sulphate. On adding solution of 

 potash, a violet colour is obtained (compare v, 2, b). 



2. Paragloblllin (Fibrino-plastin). 



a. Dilute five c.c. of serum with about seventy-five c.c. of water. Neu- 

 tralize carefully with a few drops of 0*1 per cent, sulphuric acid, and allow 

 the precipitate to settle. 



This precipitate is soluble in excess. 



b. Repeat a, passing a stream of CO 2 through the liquid, instead of neu- 

 tralizing it with weak acid. 



c. Repeat a and b without dilution. No precipitate is produced. 



3. Peptic Digestion. 



a. Introduce some fibrin into a test-tube and just cover it with 0*2 per cent, 

 solution of HC1. Allow it to stand for forty-five minutes in a water-bath at 

 from 35 to 38 C. At the end of this time the fibrin is swollen and trans- 

 parent, but has not dissolved. 



b. Repeat a, using, instead of hydrochloric acid, water to which a drop of 

 glycerine extract of pepsin has been added. 



The fibrin remains unaltered. 



c. Repeat a, adding a drop of the same extract to the acid liquid. The 

 fibrin dissolves gradually. 



d. Colour with litmus the liquid obtained in c. Neutralize carefully with 

 weak solution of caustic potash ( iii, 6). The acid albumin formed during the 

 first stage of digestion is precipitated. 



