CHEMICAL BASIS OF THE ANIMAL BODY. 45 



regard as the true pure peptones as follows 1 . The products of a 

 digestion are neutralised, filtered, very faintly acidulated with acetic 

 acid and saturated with the ammonium salt. The filtrate from the 

 precipitate thus obtained is largely freed from the excess of salt by 

 careful concentration on a water-bath. The ammonium salt is then 

 got rid of by the addition of baryta water and barium carbonate in 

 slight excess, and after filtration these reagents are finally removed by 

 the careful addition of dilute sulphuric acid. The peptone thus 

 obtained may be still further purified by precipitation with phospho- 

 tungstic acid 2 . The pure peptones thus prepared 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 

 solution are precipitated. No quantitative statements have as yet 

 been made as to their rotatory power or diffusibility. They are stated 

 to have such an affinity for water that a small portion of the dry 

 substance when moistened with water exhibits the same phenomena 

 as does phosphoric anhydride under similar conditions. They also yield 

 an intense * biuret ' reaction with caustic soda and sulphate of copper. 



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 leucin or tyrosin can be obtained by the most prolonged action of trypsin 

 on this peptone. 



Hemipeptone. Is best obtained by the action of pepsin on hemialbumose. 

 When purified and digested with trypsin it yields much leucin and tyrosin, and in 

 this respect alone does it differ from antipeptone. 



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

 action of pepsin on proteids. 



Notwithstanding the probable formation of peptones in large 

 quantities in the stomach and intestine, to judge from the results 

 of artificial digestion, a very small quantity only can be found in the 

 contents of these organs 3 . They are probably absorbed as soon as 

 formed. Another point of interest is their reconversion into other 

 forms of proteids, since this must occur to a great extent in the body. 

 We are however as yet ignorant of the manner in which this reverse 

 change is effected. 



It is now generally considered that the peptones are products of 

 the hydrolytic decomposition of the proteids from which they are 

 formed. This view is based partly upon general considerations as to 

 the probable nature of the change from observations of the conditions 



1 Zt.f. Biol Bd. xxn. (1886), S. 423. 



2 Hirschler, Zt. f. physiol. Chem. Bd. xi. (1887), S. 28. Otto, Ibid. Bd. vni. (1883), 

 S. 136. 



3 Schmidt-Miilheim, Arch. /. Physiol. 1879, S. 39. 



