RETICULIN, SKELETONS. 121 



Reticulin has the following composition: C 52.88; H 6.97; N 15.63; 

 S 1.88; P 0.34; ash 2.27 per cent. The phosphorus occurs in organic 

 combination. It yields no tyrosine on cleavage with hydrochloric acid. 

 It yields, on the contrary, sulphuretted hydrogen, ammonia, lysine, 

 arginine, and valine. On continued boiling with water, or more readily 

 with dilute alkalies, reticulin is converted into a body which is precipitated 

 by acetic acid, and at the same time phosphorus is split off. 



Reticulin is insoluble in water, alcohol, ether, lime-water, sodium 

 carbonate, and dilute mineral acids. It is dissolved, after several weeks, 

 on standing with caustic soda at the ordinary temperature. Pepsin- 

 hydrochloric acid or trypsin does not dissolve it. Reticulin responds 

 to the biuret, xanthoproteic, and ADAMKIEWICZ'S reactions, but not to 

 MILLON'S reagent. 



According to TEBB reticulin is only a somewhat changed, impure collagen 

 but this is disputed by SIEGFRIED.* 



It may be prepared as follows, according to SIEGFRIED: Digest intes- 

 tinal mucosa with trypsin and alkali. Wash the residue, extract with 

 ether, and digest again with trypsin and then treat with alcohol and ether. 

 On careful boiling with water the collagen present either as contamination 

 or as a combination with reticulin is removed. The thoroughly boiled 

 residue consists of reticulin. 



Ichthylepidin is an organic compound, so called by C. MORNER,* which occurs 

 with collagen in fish-scales and forms about one-fifth of their organic substance. 

 This compound, with 15.9 per cent nitrogen and 1.1 per cent sulphur, stands on 

 account of its properties rather close to elastin. It is insoluble in cold and hot 

 water, as well as in dilute acids and alkalies at the ordinary temperature. On 

 boiling with these it dissolves. Pepsin-hydrochloric acid, as well as an alkaline 

 trypsin solution, also dissolves it. It responds beautifully with MILLON'S reagent, 

 the xanthoproteic reaction, and the biuret test. At least a part of the sul- 

 phur is split off by the action of alkali. Ichthylepidin stands very close to elastin 

 in regard to its solubilities ; but it differs essentially in composition as it is markedly 

 poorer in glycocoll, but much richer in proline and glutamic acid than elastin 

 (ABDERHALDEN and VOITINOVICI 3 ). 



As skeletins, KRUKENBERG 4 has designated a number of nitrogenized 

 substances which form the skeletal tissue of various classes of invertebrates. 

 These substances are chitin, spongin, conchiolin, byssus, cornein, and 

 crude silk (fibroin and sericiri). Of these, chitin does not belong to the 

 protein substances, and silk is hardly to be classed as a skeletin. Only 

 those so-called skeletins will be discussed that actually belong to the pro- 

 tein group, and chitin will be discussed in another chapter. 



1 Tebb, Journ. of Physiol., 27; Siegfried, ibid., 28. 



2 Zeitschr. f. physiol. Chem., 24 and JJ7. See also Green and Tower, ibid., 35. 



3 Zeitschr. f. physiol. Chem., 52, p. 368. 



4 Grundziige einer vergl. Physiol. d. thier. Cerustsubst. Heidelberg, 1885. 



