130 THE PROTEIN SUBSTANCES. 



which are closely allied to the peptones, he calls secondary proteases. As 

 essential differences between the primary and secondary proteoses he 

 suggests the following: 1 The primary proteoses are precipitated by 

 nitric acid in salt-free solutions, while the secondary proteoses are pre- 

 cipitated only in salt solutions, and certain deuteroproteoses, such as 

 deuterovitellose and deuteromyosinose, are precipitated by nitric acid 

 only in solutions saturated with NaCl. The primary proteoses are pre- 

 cipitated from neutral solutions by copper-sulphate solution (2 : 100), 

 and by NaCl in substance, while the secondary proteoses are not. The 

 primary proteoses are completely precipitated from a solution saturated 

 with NaCl by the addition of acetic acid saturated with salt, while the 

 secondary proteoses are only partly precipitated. The primary proteoses 

 are readily precipitated by acetic acid and potassium ferrocyanide, while 

 the secondary are only incompletely precipitated after some time. The 

 primary proteoses are also, according to PicK, 2 completely precipitated 

 by ammonium sulphate (added to one-half saturation), while the secondary 

 proteoses remain in solution. 



The true peptones, as they were formerly considered to be, are exceed- 

 ingly hygroscopic, and if perfectly dry, sizzle like phosphoric anhydride 

 when treated with a little water. They are exceedingly soluble in water, 

 diffuse more readily than the proteoses, and are not precipitated by 

 ammonium sulphate. In contradistinction to the proteoses, the true 

 peptones are not precipitated by nitric acid (even in solutions saturated 

 with salt), by sodium chloride and acetic acid saturated with salt, 

 potassium ferrocyanide and acetic acid, picric acid, trichloracetic 

 acid, potassium-mercuric iodide, and hydrochloric acid. They are pre- 

 cipitated by phosphotungstic acid, phosphomolybdic acid, corrosive 

 sublimate (in the absence of neutral salts), absolute alcohol, and tannic 

 acid, but the precipitate may redissolve on the addition of an excess of 

 the precipitant. As an important difference between amphopeptone and 

 antipeptone we must also mention that the former gives MILLON'S 

 reaction, while the antipeptone does not. 



In regard to the precipitation by alcohol we must call attention to the observa- 

 tions of FRANKEL that not only are the acid combinations of peptone (PAAL) 

 soluble in alcohol, but also the free peptone, and FRANKEL has even suggested a 

 method of preparation based on this behavior. SCHROTTER 3 has also prepared 

 crystalline proteoses which were soluble in hot alcohol, especially methyl alcohol. 



The views on the hydrolytic cleavage products of peptic and tryptic 

 digestion which were accepted until a few years ago have recently been 

 considerably modified in several points. 



1 Neumeister, Zeitschr. f . Biologie, 24 and 2G. 



2 Zeitschr. f. physiol. Chem., 24. 



3 Frankel, Zur Kenntnis der Zerfallsprodukte des Eiweisses bei peptischer und 

 tryptischer Verdauung, Wien, 1896; Schrotter, Moiiatshefte f. Chem., 14 and 16. 



