Il8 PHYSIOLOGICAL CHEMISTRY 



consider them as the last product of the processes before mentioned 

 which still possess true protein characteristics. In other words, it has 

 been considered that the protein nature of the end-products of the 

 cleavage of the protein molecule ceased with the peptones, and that the 

 simpler bodies formed from peptones were substances of a different 

 nature (see page 64). However, as the end-products have been more 

 carefully studied, it has been found to be no easy matter to designate 

 the exact character of a peptone or to indicate the exact point at 

 which the peptone characteristic ends and the peptide characteristic 

 begins. The situation regarding the proteoses, peptones and peptides 

 is at present a most unsatisfactory one because of the unsettled state 

 of our knowledge regarding them. The exact differences between 

 certain members of the peptone and peptide groups remain to be more 

 accurately established. ^ It has been quite well established that the 

 peptones are peptides or mixtures of peptides, but the term peptide is 

 used at present to designate only those possessing a definite structure. 

 There are several proteoses (protoproteose, heteroproteose and 

 deuteroproteose), and at least two peptones (amphopeptone and anti- 

 peptone), which result from proteolysis. The differentiation of the 

 various proteoses and peptones at present in use is rather unsatisfactory. 

 These compounds are classified according to their varying solubilities, 

 especially in ammonium sulphate solutions of different strengths. The 

 exact differences in composition between the various members of the 

 group remain to be more accurately established. Because of the 

 difficulty attending the separation of these bodies, pure proteose and 

 peptone are not easy to procure. -The so-called peptones sold com- 

 mercially contain a large amount of proteose. As a class the proteoses 

 and peptones are very soluble, diffusible bodies which are non-coagu- 

 lable by heat. Peptones differ from proteoses in being more diffusible, 

 non-precipitable by (NH 4 ) 2 S04, and by their failure to give any reaction 

 with potassium ferrocyanide and acetic acid, potassio-mer curie iodide 

 and HC1, picric acid, and trichlor acetic acid. Peptones may be pre- 

 cipitated by phosphotungstic acid, phosphomolybdic acid, absolute 

 alcohol and tannic acid, but an excess of the precipitant may dissolve 

 the precipitate. The so-called primary proteoses are precipitated by 

 HN0 3 and are the only members of the proteose-peptone group which 

 are so precipitated. 



Some of the more general characteristics of the proteose-peptone group may 

 be noted by making the following simple tests on a proteose-peptone powder : 



(1) Solubility. Solubility in hot and cold water and sodium chloride solution. 



(2) Millon's Reaction. 



Dissolve a little of the powder in water and test the solution as follows : 



