118 



THE PROTEIN SUBSTANCES. 



with water, and lastly with acetic acid. The residue is treated with cold 

 5 per cent hydrochloric acid for twenty-four hours, carefully washed 

 with water, boiled again with water, and then treated with alcohol and 

 ether. 



In regard to the methods used by SCHWARZ and by RICHARDS and GIES, which 

 are somewhat different, we refer to the original publications. 



Collagen, or gelatin-forming substance, occurs very extensively in 

 vertebrates. The flesh of cephalopods is also said to contain collagen. 1 

 Collagen is the chief constituent of the fibrils of the connective tissue and 

 (as ossein) of the organic substances of the bony structure. It also occurs 

 in the cartilaginous tissues as chief constituent; but it is here mixed 

 with other substances, producing what was formerly called chondrigen. 

 Collagen from different tissues has not quite the same composition, and 

 probably there are several varieties of collagen. 



By continued boiling with water (more easily in the presence of a 

 little acid) collagen is converted into gelatin. HOFMEISTER 2 found that 

 gelatin on being heated to 130 C. is again transformed into collagen; 

 and this last may be considered as the anhydride of gelatin. Collagen 

 and gelatin have about the same composition. 3 



Collagen 



Gelatin (commercial) . . . 

 Gelatin from tendons. . . 

 Gelatin from ligaments. . 

 Fish glue (isinglass) .... 



50.75 

 49.38 

 50.11 

 50.49 

 48.69 



H 



6.47 

 6.80 

 6.56 

 6.71 

 6.76 



N 



17.86 

 17.97 

 17.81 

 17.90 

 17.68 



24.92 



0.70 25.13 

 0.26 25.26 

 0.57 24.33 



(HOFMEISTER) 

 (CHITTENDEN) 

 (VAN NAME) 

 (RICHARDS and GIES) 

 (FAUST) 



Gelatins of different origin show a somewhat variable composition, 

 which seems to indicate the occurrence of different collagens. It is diffi- 

 cult to say whether the variable content of sulphur is due to a contami- 

 nation with a substance rich in sulphur or to a splitting off of loosely 

 combined sulphur during the purification. C. MORNER* has prepared 

 a typical gelatin containing only 0.2 per cent of sulphur by a method 

 which eliminated any possible changes due to reagents. 



SADIKOFF 5 has prepared gelatins by various methods from tendons and 

 from cartilage. Those from tendons, some of which were prepared after pre- 

 vious tryptic digestion, some after treatment with 0.25 per cent caustic potash, 

 and some after treatment with sodium hydroxide and then carbonate, showed 



1 Hoppe-Seyler, Physiol. Chem., p. 97. 



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



3 Hofmeister, 1. c.; Chittenden and Solley, Journ. of Physiol., 12; van Name, 

 Journ. of Exper. Med., 2; Richards and Gies, Amer. Journ. of Physiol., 8; Faust, 

 Arch. f. exp. Path. u. Pharm., 41. 



4 Zeitschr. f. physiol. Chem., 28. 



5 Ibid., 39 and 41. 



