CHEMICAL BASIS OF THE ANIMAL BODY. 1185 



to their behaviour towards neutral ammonium sulphate. The 

 albumoses are precipitated when their solutions are saturated 

 with this salt, and the true peptones are characterized as those 

 final products of the digestion which are not precipitable by the 

 ammonium salt. The peptones are thus obtained in the filtrate 

 from the saturated solution and may be separated from the excess 

 of admixed salt by processes which are tedious and admit of no 

 suitably brief description. 



The general properties and reactions of peptones as thus 

 obtained may be stated as follows. Precipitated by alcohol 

 they consist of a white or yellowish powder, which is hygro- 

 scopic and extraordinarily soluble in water, and hence often 

 deliquescent. Unless thoroughly dehydrated the powder may 

 melt on gentle warming. They have such an affinity for water 

 that a small portion of the dry substance when moistened hisses 

 as does phosphoric anhydride under similar conditions. From 

 their neutral aqueous solutions they are precipitated with diffi- 

 culty by a large excess of alcohol, being unchanged in the 

 process and riot becoming coagulated or insoluble by prolonged 

 exposure to the action of the precipitant. The precipitation 

 occurs with difficulty if at all in presence of hydrochloric 

 acid. Peptones are strikingly non-precipitable by many of the 

 reagents by which other proteids may be precipitated, more 

 especially by ferrocyanide of potassium in presence of acetic 

 acid, a reagent by which practically all other proteids in solu- 

 tion are precipitated, but are precipitated by tannic acid, mer- 

 curic chloride, nitrates of mercury, and by phosphotungstic and 

 phosphomolybdic acids in presence of hydrochloric or other 

 mineral acids; also by the double iodides of potassium and 

 mercury or potassium and bismuth, in presence of strong 

 mineral acids. A very characteristic reaction is the 'biuret ' 

 or pink coloration which is obtained on the addition of an 

 excess of caustic soda and a mere trace of sulphate of copper. 

 The slightest excess of the copper salt gives a violet colour, 

 as is the case with all other proteids, which deepens in tint on 

 boiling. This biuret reaction is however yielded also by the 

 albumoses but to a less striking degree (see above). Peptones 

 are all leevorotatory and more diffusible than the albumoses. 



Amphopeptone. This is the mixture of anti- and hemi-peptone 

 resulting from the action of pepsin on proteids. 



Antipeptone may be obtained by the action of either pepsin or 

 trypsin on antialbumose, or by the action of trypsin on antialbumate 

 or antialbumid. When purified no leucine or tyrosine can be obtained 

 by the most prolonged action of trypsin on this peptone. 



Hemipeptone. Although occurring in amphopeptone, it cannot as 

 yet be separated with any precision from the antipeptone with which 

 it is mixed. 



Notwithstanding the probable formation of peptones in large 



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