PROPERTIES OF PEPTONES. 333 



to crystallise (Drechsel). (3) They filter quite easily through the 

 pores of animal membranes (Acker). (4) They are not precipitated by 

 "boiling nitric acid, acetic acid and potassium ferrocyanide, weak alcohol, 

 or metaphosphoric acid. (5) They are precipitated from neutral or 

 feebly acid solutions by mercuric chloride, mercuric nitrate [Millon's 

 reagent], silver nitrate, basic lead acetate, potassio-mercuric iodide, 

 tannic acid, picric acid, bile acids, strong alcohol, phosphoro-wolframic 

 acid, and phosphoro-molybdic acid (Briicke). (6) With Millon's 

 reagent they react like proteids, and give a red colour, and with nitric 

 acid give the yellow xantho-protein reaction. (7) With caustic potash 

 or soda and a small quantity of cupric sulphate, they give a beautiful 

 purplish-red colour (Biuret-reaction). (8) They rotate the plane of 

 polarised light to the left. 



The biuret-reaction is obtained with propeptone, as well as with a form of 

 albumin, which is formed during artificial digestion and is soluble in alcohol. It 

 is called Alkophyr by Briicke. 



[Darby's fluid meat gives all the above reactions, and is very useful 

 for studying the tests for peptones.] 



Preparation. Pure peptones are prepared by taking fluid which contains 

 them and neutralising it with barium carbonate, evaporating upon a water-bath, 

 and filtering. The barium is removed from the filtrate by the careful addition of 

 sulphuric acid, and subsequent filtration (Hoppe-Seyler). Brieger extracted from 

 gastric peptones by amylic alcohol a peptone-free poison, with actions like those of 

 curara. It belongs to the group of ptomaines i.e. , alkaloids obtained from dead 

 bodies. 



Peptones are undoubtedly those modifications of albumin or proteids 

 which, after their absorption from the intestinal canal into the blood, 

 are destined to be used to make good the proteids used up in the 

 human organism. By giving peptones (instead of albumin) as food, 

 life can not only be maintained, but there may even be an increase of 

 the body-weight (Pl6sz and Maly, Adamkiewicz). 



The N-equilibrium in the metabolism of the body may be kept up 

 by administering I'll grammes of peptones, artificially prepared from 

 flesh, per kilo, of the body-weight (Catillon). After being absorbed 

 into the blood-stream, peptones are retransformed, first into propeptone, 

 and then into serum-albumin. 



Conditions Affecting Gastric Digestion. The presence of already-formed 

 peptones interferes with the action of the gastric juice, in so far as the greater 

 concentration of the fluid interferes with and limits the mobility of the fluid par- 

 ticles (Hoppe-Seyler). Boiling concentrated acids, alum, and tannic acid, alkalinity 

 of the gastric juice (e.g., by the admixture of much saliva) abolish the action. 

 The salts of the heavy metals, which cause precipitates with pepsin, peptone, 

 and mucin, interfere with gastric digestion, and so do concentrated solutions of 

 alkaline salts, common salt, magnesium and sodium sulphates. Alcohol precipi- 

 tates the pepsin, but by the subsequent addition of water it is redissolved, so that 



