PROPERTIES OF PEPTONES. 



249 



pepsin can dissolve new quantities of albumin. Still, it seems that some pepsin is 

 used up in the process of digestion (Griitzner), Proteids are introduced into the 

 stomach either in a solid (coagulated) or fluid condition. Casein alone of the 

 fluid forms is precipitated or coagulated, and afterwards dissolved. The non- 

 coagulated proteids are transformed into syntonin, without being previously 

 coagulated, and are then changed into pro-peptone and directly peptonised, i.e., 

 actually dissolved. 



When albumin is digested by pepsin at the temperature of the body, a not inconsiderable 

 amount of heat disappears, as can be proved by calorimetric experiment (Maly). Hence, the 

 temperature of the chyme in the stomach falls 0"2 to 0*6 C. in two to three hours (v. Vintschgau 

 and Dietl). " - 



Coagulated albumin may be regarded as the anhydride of the fluid form, and the 

 latter again as the anhydride of peptone. The peptones, therefore, represent the 

 highest degree of hydration of the proteids. 



Hence, peptones may be formed from proteids by those reagents which usually cause hydra- 

 tion, viz., treatment with strong acids (from fibrin, with 0*2 HC1), caustic alkalies, putrefactive 

 and various other ferments, and ozone. 



The anhydride proteid has been prepared from the hydrated form. Henniger 

 and Hofmeister, by boiling pure peptone with dehydrating substances (anhydrous 

 acetic acid at 80 C), have succeeded in decomposing it into a body resembling 

 syntonin. 



Peptones. (1) They are completely soluble in water. (2) They diffuse very 

 easily through membranes. (3) They filter quite easily through the pores of animal 

 membranes. (4) They are not precipitated by boiling, nitric acid, acetic acid and 

 potassium ferrocyanide, acetic acid and saturation with common salt. (5) They 

 are precipitated from neutral or feebly acid solutions by mercuric chloride, tannic 

 acid, bile acids, and phosphoro-molybdic acid. (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, [or Fehling's solution], they give a beautiful rosy-red colour, the biuret- 

 reaction. (8) They rotate the plane of polarised light to the left. 



[Kuhne and Chittenden, making use of the fact that ammonium sulphate to 

 saturation precipitates all proteids from solution except peptone, have reinvestigated 

 the subject, and they find that many of the peptones of commerce contain albumoses. 

 Pure peptone has remarkable properties. When dissolved in water, it hisses and 

 froths like phosphoric anhydride, heat is evolved, and a brown solution is formed. 

 It is difficult to preserve it. It is not precipitated by NaCl, or NaCl and acetic 

 acid, but is completely precipitated by phospho-tungstic and phospho-molybdic 

 acids, tannin, iodo-mercuric iodide, picric acid. Peptones have a cheesy taste, while 

 albumin and albumoses are tasteless.] 



The biuret-reaction is obtained with pro-peptone, 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.] 



The rapidity of solution of fibrin is tested by placing fibrin, which is swollen up by the 

 action of 0*2 per cent. HC1 in a glass funnel, and adding the digestive fluid, observing the 

 rapidity with which the fluid, the altered fibrin, drops from) the funnel, and the fibrin disappears 

 (Grunhagen). Or the fibrin maybe coloured with carmine, swollen up in 0*1 per cent. HCI, 

 and placed in the digestive fluid. The more rapidly the fluid is coloured red, the more energetic 

 is the digestion. 



Preparation. Pure peptones are prepared by taking fluid which contains them and neutralis- 

 ing 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. 



Ptomaines. 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 or decomposing proteids. [Ptomaines are identical with the alkaloids in 

 plants, and many have been isolated. The term leucomaine has been applied by Gautier to 



