DIGESTION OF CASEIN. 619 



obtained also varies considerably. SALKOWSKI considers that the quar- 

 tity of pseudonuclein split off is dependent upon the relation between 

 the casein and the digestion fluid, e.g., the quantity of the pseudonu- 

 cleins diminishes as the pepsin-hydrochloric acid increases. In the presence 

 of 500 grams of pepsin-hydrochloric acid to 1 gram of casein SALKOWSKI 

 digested the latter completely without obtaining any pseudonuclein. 



In peptic as well as tryptic digestion a part of the organic phosphorus 

 is split off as orthophosphoric acid, the quantity increasing as the digestion 

 progresses. Another part of the phosphorus is retained in orgajiic com- 

 bination in the proteoses as well as in the true peptones (SALKOWSKI, 

 BIFFI, ALEXANDER, ADERS PLIMMER and BAYLISS 1 ). 



From the products of peptic digestion of casein, after the separation 

 of the pseudonuclein, SALKOWSKI 2 has isolated an acid rich in phos- 

 phorus. He considers this a paranudeic acid. It is soluble in water, 

 insoluble in alcohol, levorotatory, and contained N 13.25-13.55, and P 

 4.05^.31 per cent. The acid differs from the nucleic acids in that it 

 gives the biuret test and a faint xanthoproteic reaction. Presupposing 

 its purity, it is not an acid comparable with the nucleic acids. A still 

 richer product in phosphorus, with 6.9 per cent P, has been isolated 

 as a uranium compound by REH S from the peptic digestive products 

 of casein. He calls this body polypeptid phosphoric acid. On hydrolysis 

 this product gave 18.7 per cent nitrogen as diamino-acids, 56.7 per cent 

 as monamino-acids and the remarkably high result 23.8 per cent amido- 

 nitrogen. This pseudonucleic acid also gave the biuret and the xantho- 

 proteic tests and MILLON'S reaction, and behaved like a protein rich in 

 phosphorus. 



Casein may be prepared in the following way: The milk is diluted 

 with 4 vols. of water and the mixture treated with acetic acid to 0.75 

 1 p. m. Casein thus obtained is purified by repeatedly dissolving in water 

 with the aid of the smallest quantity of alkali possible, by filtering and 

 reprecipitating with acetic acid and thoroughly washing with water. Most 

 of the milk-fat is retained by the filter on the first filtration, and the 

 casein contaminated with traces of fat is purified by treating with alcohol 

 .and ether. 



Lactoglobulin was obtained by SEBELIEN from cow's milk by saturating 

 it with NaCl in substance (which precipitated the casein) and saturating 

 the filtrate with magnesium sulphate. As far as it has been investigated 



59; Salkowski, ibid., 63; v. Moraczewski, Zeitschr. f. physiol. Chem., 20; Sebelien 

 ibid., 20; Zaitschek, Pfliiger's Arch., 104. 



Salkowski, 1. c.; Biffi, Virchow's Arch., 152; Alexander, Zeitschr. f. physiol. 

 Chem., 25; Plimmer and Bayliss, Journ. of Physiol., 33. 



2 Zeitschr. f. physiol. Chem., 32. 



3 Hofmeister's Beitrage, 11. 



