120 THE PROTEIN SUBSTANCES. 



a deutero-gelatose, besides a true peptone. The elementary composition 

 of these gelatoses does not essentially differ from that of the gelatin. 



According to LEVENE the proto- as well as the deuterogelatoses yield 

 a larger amount of glycocoll than the gelatin itself. On prolonged tryptic 

 digestion a further demolition takes place, so that the peptone yields 

 only about the same amount of glycocoll as the gelatin. Some leucine 

 and, as it appears, also some glutamic acid and phenylalanine are split 

 off. Quite a considerable splitting off of NH 3 also takes place (LEVENE 

 ard STOOKEY). 1 



PAAL 2 has prepared gelatin-peptone hydrochlorides from gelatin by the 

 action of dilute hydrochloric acid. These salts are partly soluble in ethyl and 

 methyl alcohol, and partly insoluble therein. The peptones obtained from 

 these salts contain less carbon and more hydrogen than the gelatin from which 

 they originated, showing that hydration has taken place. The molecular weight 

 of the gelatin peptone as determined by PAAL, by RAOULT'S cryoscopic method, 

 was 200 to 352, while that for gelatin was 878 to 950. The gelatin peptones 

 isolated by SIEGFRIED and his pupils SCHEERMESSER and KRUGER and w T hich 

 will be discussed below, are of great interest. 



Collagen (contaminated with mucoid) may be obtained from bones by 

 extracting them with hydrochloric acid (which dissolves the earthy 

 phosphates) and then carefully washing the acid out with water. It may 

 be obtained from tendons^by extracting with lime-water or dilute alkali 

 (which dissolve the proteids and mucin) and then thoroughly washing 

 with water. Gelatin is obtained by boiling collagen with water. The 

 finest commercial gelatin always contains a little proteid, which may 

 be removed by allowing the finely divided gelatin to swell up in water 

 and thoroughly extracting with large quantities of fresh water. Then 

 dissolve in warm water and precipitate with alcohol. 



Collagen may also be purified from proteids, as suggested by VAN NAME, 

 by digesting with an alkaline trypsin solution or by extracting the gela- 

 tin for many days with 1-5 p. m. caustic potash, as suggested by C. 

 MORNER. The typical properties of gelatin are not changed by this. 

 



Chondrin or cartilage gelatin is only a mixture of gelatin with the specific 

 constituents of the cartilage and their transformation products. 



Reticulin. The reticular tissues of the lymphatic glands contain a 

 variety of fibers which have also been found by MALL in the spleen, intes- 

 tinal mucosa, liver, kidneys, and lungs. These fibers consist of a special 

 substance, reticulin, investigated by SIEGFRIED. 3 



1 Levene, Zeitschr. f. physiol. Chem., 37; Levene and Stookey, ibid., 41. 



2 Ber. d. deutsch. chem. Gesellsch., 25. 



3 Mall, Abhandl. d. math.-phys. Klasse d. Kgl. sachs. Gesellsch. d. Wiss., 1891; 

 Siegfried, Ueber die chem. Eigensch. der retikulirten Gewebe, Habil.-Schrift, Leipzig, 

 1892. 



