CII. XXXIII. ] 



PRQTEOSES AND PEPTONES 



515 



2. Proteoses. They are not coagulated by heat ; they are pre- 

 cipitated but not coagulated by alcohol : like peptone, they give the 

 pink biuret reaction. They are precipitated by nitric acid, the pre- 

 cipitate being soluble on heating, and reappearing when the liquid cools. 

 This last is a distinctive property of proteoses. They are slightly 

 diffusible. 



The primary proteoses are precipitated by saturation with 

 magnesium sulphate or sodium chloride. Deutero-proteose is not; 

 it is, however, precipitated by saturation with ammonium sulphate. 

 Proto- and deutero-proteose are soluble in water ; hetero-proteose is 

 not ; it requires salt to hold it in solution. 



3. Peptones. They are soluble in water, are not coagulated by heat, 

 and are not precipitated by nitric acid, copper sulphate, ammonium 

 sulphate, and a number of other precipitants of proteins. They are 

 precipitated but not coagulated by alcohol. They are also precipi- 

 tated by tannin, picric acid, potassio-mercuric iodide, phospho- 

 molybdic acid, and phospho-tungstic acid. 



They give the biuret reaction (rose-red solution with a trace of 

 copper sulphate and caustic potash or soda). 



Peptone is readily diffusible through animal membranes. 



The annexed table will give us at a glance the chief characters of 

 peptones and proteoses in contrast with those of the native proteins, 

 albumins, and globulins. 



In the case of deutero-albumose this reac.ion only occurs in the presence of >xcess of salt. 



