BY DR. LAUDER BRUNTON. 485 



drop of litmus in the filtrate and neutralize it; a precipitate 

 of syntonin or parapeptone will fall. Filter the liquid: the 

 neutral filtrate containing peptones will not be precipitated by 

 boiling, but it will give the xanthoprotein reaction strongly, 

 and will give a precipitate with tannin. 1 



For the further examination of the products of digestion, 

 filter the solution in the beaker from any undissolved residue. 

 Neutralize, and parapeptones will be precipitated. Let the 

 precipitate settle, and then filter : the filtrate will contain pep- 

 tones. Test for a and 6 peptones. If they are present, put 

 the beaker back in the bath for a while, and then test for 

 them again. If they are no longer present, apply the follow- 

 ing tests: 



** 118. Reactions of Peptones. True or c peptones 

 possess the following characteristics : They are not precipitated 

 by (1) neutralization, (2) boiling the solution, either neutral 

 or acid, (3) nitric acid either in the cold or on boiling, (4) 

 hydrochloric acid in the cold, (5) acetic acid and potassium 

 ferrocyanide (after standing, the fluid becomes turbid and 

 gives a precipitate) (6) copper sulphate in small quantity 

 (if more is added it causes turbidity, which partly disappears 

 on adding excess). They are precipitated by (1) tannic acid, 

 (2) silver nitrate, (3) mercuric chloride, (4) platinum chloride, 

 (5) lead acetate, both neutral and basic. (The precipitate is 

 soluble in excess.) 



The solution, when treated with caustic potash and an 

 extremely minute quantity of copper sulphate, or a drop of 

 diluted Fehling's solution, gives a precipitate which dissolves 

 on shaking, and forms a red solution. If more copper sul- 

 phate is then added, it becomes violet. Peptones thus differ 

 from albumin, which gives a violet at once. 



** 119. Diffusibility of Peptones. Put a solution of 

 peptones into a small dialyzer, and let it diffuse into distilled 

 water for an hour or two. Then test the water by the tests 

 given above, and peptones will be found to be present. In 

 this they differ from albumin, which, as has been already seen, 

 hardly diffuses at all. 



* 120. Action of Gastric Juice on Gelatin. Pepsin, 

 with dilute hydrochloric acid, deprives gelatin of its power to 



1 For showing the action of pepsin to a class, Grunhagen's method 

 may be employed. A piece of moist fibrin is placed in 0.2 per cent, 

 hydrochloric acid till it swells to a stiff jelly. It is then laid on a funnel, 

 either with or without a filter, and after the superfluous acid has drained 

 off, a few drops of glycerin solution of pepsin, or artificial gastric juice, 

 are added to it. The rapidity with which the fibrin is converted into 

 peptone is shown by the number of drops which fall from the funnel. 

 By using two similar filters, the power of different digestive fluids may 

 be compared, and the effect of temperature shown by using Planta- 

 mour's funnel. 



