132 THE PROTEIN SUBSTANCES. 



tryptic digestion, and these bodies resist the prolonged action of the 

 enzyme, but yield several different amino-acids on hydrolytic cleavage by 

 acids. The same is probably also true for peptic digestion (see below), 

 and the difference in the digestive products between pepsin and trypsin 

 digestion consists, essentially, only in that, in the first case the cleavage 

 is slower and does not proceed so far, hence the biuret reaction remains 

 and generally no formation of tryptophane takes place. 



By the use of the methods specially worked out by the HOFMEISTER 

 school, of fractionally salting out with ammonium sulphate or zinc sul- 

 phate or also by SIEGFRIED'S iron-alum method, numerous attempts to 

 separate the various proteoses and peptones have recently been made 

 by UMBER, ALEXANDER, PFAUNDLER, PICK, ZUNZ, SIEGFRIED and his 

 pupils. 1 Not only have we learned by these methods of a larger number 

 of proteoses, but our older conception of the products formed primarily 

 has been materially modified. Immediately at the commencement 

 of digestion, even in peptic digestion, a splitting of the protein molecule 

 into several complexes takes place. In opposition to the view of HuppERT, 2 

 that the proteoses, in pepsin digestion, are always derived from the pri- 

 marily formed acid albuminate, PICK and ZUNZ have shown that several 

 proteoses, as well as acid albuminate, appear as primary products at the 

 commencement of the digestion. According to GOLDSCHMIDT 3 a splitting 

 off of proteoses and the formation of acid albuminate takes place simul- 

 taneously by the action of dilute acids alone. Besides the proteoses 

 we also have, according to ZUNZ and PFAUNDLER, even at the beginning, 

 other primary bodies, which cannot be salted out and which do not 

 give the biuret reaction, but are in part precipitated by phosphotungstic 

 acid. These little -known products seem to be intermediate between 

 the peptones and the amino-acids, and they correspond probably to the 

 polypeptide bodies obtained by FISCHER and ABDERHALDEN in tryptic 

 digestion. 



By fractional precipitation of WITTE'S peptone with ammonium sulphate 

 PICK has obtained various chief fractions of proteoses. The first contains the 

 proto- and heteroproteoses whose precipitation limit lies at 24-42 per cent satu- 

 ration with ammonium sulphate solution, i.e., the presence of 24-42 cc. of the 

 saturated ammonium sulphate solution in 100 cc. of the liquid. Then follows 

 a fraction A at 54-62 per cent saturation, then a third fraction B, with 70-95 

 per cent saturation, and finally fraction C, which precipitates from the saturated 

 solution on acidification with sulphuric acid saturated with the salt. 



1 Umber, Zeitschr. f. physiol. Chem., 25; Alexander, ibid., 25; Pfaundler, ibid., 

 30; Zunz, ibid., 28, and Hofmeister's Beitrage, 2; Pick, ibid., 2, and Zeitschr. f. physiol. 

 Chem., 24 and 28; Siegfried, see footnote 2, page 135. 



2 Schiitz and Huppert, Pfliiger's Arch., 80. 



3 F. Goldschmidt, Ueber die Einwirkung von Sauren auf Eiweissstoffe, Inaug.- 

 Diss. Strassburg, 1898. 



