APPENDIX. 739 



CLASS V. 



Peptone. Peptone is formed by the action of the digestive ferments, 

 pepsin, or trypsin, on other proteids, and on gelatin. 



The properties and tests for peptone are at present very unsatisfac- 

 tory, owing to the fact that the substance can be obtained in a pure con- 

 dition with extreme difficulty. Many of the following tests, therefore, 

 which are usually given for the substance, are very likely due to impuri- 

 ties, intermediate digestion products, or albumose. A solution of com- 

 mercial peptone in water gives the following tests: 



It is not coagulated on heating; it is not precipitated by saturation 

 with NaCl, or MgS0 4 , or by C0 a . It is not precipitated by boiling with 

 sodium sulphate and acetic acid. It is not precipitated by addition of 

 dilute acid or alkali. It is precipitated from neutral or slightly acid solu- 

 tions by: 



Mercuric chloride, the precipitate being only partly soluble in 

 excess; argentic nitrate; lead acetate; potassio-mercuric iodide; 

 bile salts; phosphoro-molybdic acid; tannin, the precipitate 

 being soluble in dilute acid, but not in excess of the reagent. 

 Picric acid (saturated solution), the precipitate disappears on 

 heating, and partly returns on cooling. It is precipitated, but 

 not coagulated by absolute alcohol, and by ether. The solution 

 of impure peptone gives 



The Xanthoproteic reaction easily, but there is very slight, if any 

 previous precipitation with the nitric acid. 



The Biuret reaction but the color is pink instead of violet. 



With Millon's test not so easily as do native albumins. 



With Ferrocyanide and acetic acid only in cases where the pep- 

 tone is very impure, is there any precipitate. 



The only substance which appears to separate the whole of the other 

 proteids from peptone is ammonium sulphate. 

 It dialyzes freely. 



CLASS VI. 



Coagulated proteids are formed by the action of heat upon other 

 proteids; the temperature necessary in each case varying in the manner 

 previously indicated. They may also be produced by the prolonged ac- 

 tion of alcohol upon proteids. 



They are soluble in strong acids or alkalies; slightly so in dilute; are 

 soluble in digestive fluids (gastric and pancreatic). Are insoluble in saline 

 solutions. 



CLASS VII. 



Lardacein is found in organs which are the seat of amyloid degenera- 

 tion. 



