124 THE PROTEIN SUBSTANCES. 



is identical with 3-5 di-iodo-tyrosine, HOI 2 C 6 H2.CH2.CHNH2COOH, 

 synthetically prepared by WHEELER and JAMIESON. 1 On acid cleavage 

 of gorgonin, HENZE 2 obtained the three hexone bases, abundant tyrosine 

 and very little leucine. On cleavage with barium hydroxide he obtained 

 only lysine, besides tyrosine and glycocoll in larger amounts. 



Fibroin and sericin are the two chief constituents of raw silk. By 

 the action of boiling water the sericin (silk gelatin) dissolves and can be 

 obtained by a method suggested by BoNDi, 3 while the more difficultly 

 soluble fibroin remains undissolved in the shape of the original fiber. 

 The sericin, whose sufficiently concentrated hot solution gelatinizes on 

 cooling, is precipitated by mineral acids, several metallic salts, and by 

 acetic acid and potassium ferrocyanide. The spider silk investigated 

 by FISCHER 4 yielded fibroin but not sericin. 



ABDERHALDEN and his collaborators 5 have investigated a great 

 number of varieties of silk and found sericin in varying amounts (15 to 

 28 per cent). The composition of the various kinds of silk is char- 

 acterized, especially, by a varying amount of glycocoll and in this regard 

 we can differentiate between two chief groups. The one group is, like 

 the Italian silk, very rich in glycocoll while the other group, like the 

 Tussah silk, contains a much smaller quantity of glycocoll. 



Sericin, whose proper concentrated warm solution gelatinizes on 

 cooling, is precipitated by mineral acids and several metallic salts and 

 by acetic acid and potassium ferrocyanide. In regard to the products 

 of hydrolysis it differs very essentially from fibroin by being much poorer 

 in glycocoll, alanine and tyrosine. 



Fibroin is soluble in concentrated acids and alkalies and reprecipitable 

 (in a modified form) on neutralization. It gives the biuret test and 

 MILLON'S and ADAMKIEWICZ-HOPKIN'S reactions, the last but faintly. 

 Fibroin has an especially great interest because of the hydrolyses per- 

 formed by FISCHER and his co-workers, and especially by the finding of 

 the previously mentioned polypeptides by these workers. Of the cleavage 

 products which characterize fibroin we must mention the large amount 

 of glycocoll, alanine and tyrosine, and the very small amounts of hexone 

 bases, besides the almost complete absence of monamino-dicarboxylic 

 acids. The quantity of the hydrolytic cleavage products of the three 

 silk substances, in so far as they have been investigated, are given in the 

 following table, which also includes the results for elastin, gelatin, and 



1 Wheeler and Jamieson, Amer. Chem. Journ., 23; \7heeler, ibid., 



2 Henze, Zeitschr. f. physiol. Chem., 38 and 51. 



8 Zeitschr. f. physiol Chem., 34. 



4 Ibid., 53. 



6 See Zeitschr. f. physiol. Chem., 59, 61, 62, 64, 71, 74, 80. 



