578 CHEMISTRY OF THE PROTEIDS CHAP. 



chorda dorsalis of the lamprey is poor in firm constituents and that 

 mucin and collagen are absent; but it contains a body, not readily 

 soluble in acids, and more soluble in alkalies, which can be digested by 

 pepsin and trypsin. Kossel l has investigated the chorda dorsalis of 

 the sturgeon, and has found neither gelatine nor mucin nor mucoid, but 

 an albuminous substance which is fairly readily soluble in alkalies, 

 which is precipitated by acids, and readily digested by pepsin. 



Ichthylepidin is the name which Morner 2 gave to a substance 

 he found in fish scales besides collagen. It is insoluble in boiling 

 water, and is also only partly soluble in superheated steam. It is 

 soluble in dilute hot, and in strong cold, acids and alkalies. It is 

 digested by pepsin and by trypsin. It gives the biuret-, xanthoproteic-, 

 lead-sulphide tests and an especially well-marked Millon's reaction, 

 which latter distinguishes it from gelatine. It does not give the 

 Adamkiewicz reaction, nor does it yield a carbohydrate. It amounts 

 to 20 per cent in the scales of the teleostean fishes, and is absent in 

 the Ganoids. Amongst the Teleosts it is only absent in the Schleie. 3 

 Green and Tower 4 have also studied its distribution. 



Keratinoid. The horny layer of the muscular stomach of birds 

 has been examined by Hedenius, 5 who obtained a substance which was 

 insoluble in water, dilute acids and alkalies, and which could only be 

 dissolved by strong alkalies. Pepsin digests it slowly, while trypsin 

 has no action. Superheated steam does not render it soluble. It 

 contains sulphur, and gives the xanthoproteic-, furfurol-, and Millon's 

 reactions. When dissociated it yields leucin, a little tyrosin, but no 

 reducing substance. It differs from the keratins in possessing less 

 sulphur and less tyrosin. 



Eeticulin was prepared by Siegfried 6 from the reticular tissue of 

 the mucous membrane of the intestine, where it occurs along with 

 collagen. The mucous membrane of the small intestine of the pig is 

 first thoroughly digested with trypsin + soda, and then with boiling 

 water to remove all traces of gelatine, of the cell constituents, etc. 

 There is left over, finally, a powder, the reticulin, which is insoluble in 

 water, in dilute acids and alkalies, in pepsin and trypsin ; it contains 

 large amounts of sulphur, and in addition also phosphorus in an organic 

 form. 



A. Kossel, Zeitschr. f. physiol. Ohem. 15. 331 (1891). 

 C. T. Morner, ibid. 24. 125 (1897). 

 C. T. Morner, ibid. 37. 88 (1902). 

 E. H. Green and E. W. Tower, ibid. 35. 196 (1902). 

 J. Hedenius, Skandinav. Arch. f. Physiol. 3. 244 (1891). 

 6 M. Siegfried, Sitzungsber. d. sacks. Ges. d. Wissensch. 1892 (preliminary com- 

 munication) ; Habilitationschrift, Leipzig, 1892 ; Journ. of Physiol. 28. 319 (1902). 



