546 CHEMISTRY OF THE PROTE1DS CHAP. 



is removed with sulphuretted hydrogen and the filtrate freed from 

 salts by dialysis. Finally, the solution is strongly inspissated, and 

 after the addition of some sodium chloride precipitated with alcohol. 

 Schmiedeberg digests the cartilage he used the nasal septum of the 

 pig with pepsin-hydrochloric acid, and thus obtains a doughy residue 

 consisting of collagen and chondro-sulphuric acid. The acid is then 

 converted into the cupric oxide potash salt. 



3. The Mucoids of the Vitreous Humour, the Cornea, and the Umbilical 



Cord 



Virchow 1 was the first to notice that mucin-like substances occur 

 in the vitreous of the eye and in the umbilical cord. The mucoid of 

 the vitreous was then investigated by Morner 2 and Halliburton and 

 Young. 3 Although the mucoid amounts to only 0*1 per cent of the 

 vitreous humour, it yet conditions the physical properties of the humour, 

 which resembles a very thin jelly. It gives the ordinary mucin- 

 reactions ; acetic acid precipitates it from solutions poor in salts ; 

 alkalies dissolve the precipitate ; the alkaloidal reagents and some of 

 the heavy metals cause precipitation, as do also potassium ferro- 

 cyanide + acetic acid and nitric acid. It gives all the ordinary colour^ 

 reactions, except Liebermann's reaction, showing that the presence of 

 tryptophane is not well marked. Sodium chloride salts it out from 

 acid solutions, and magnesium sulphate also from neutral solutions. 

 According to Young, heating from 70-72 in slightly acid solutions 

 causes denaturalisation. 



The vitreous humour contains, in addition to mucoid, also traces of 

 albumin. 



The mucoid of the cornea has been prepared and analysed by 

 Morner. 4 It resembles the mucins as regards precipitability by acetic 

 acid ; it is precipitated by the alkaloidal reagents, except by ferro- 

 cyanic acid, and by the salts of the heavy metals except by corrosive 

 sublimate, etc. The ground substance of the cornea contains 20, and 

 that of the sclerotic coat 1 3 per cent of mucoid ; the remainder is 

 collagen (compare with p. 565). 



The mucoid of the umbilical cord has been studied by Jernstrom 5 

 and Young. 3 It possesses the ordinary character of the mucins ; the 

 carbohydrate radical is readily split off by 2 per cent hydrochloric 



1 Eud. Virchow, Virdww's Archiv, 4. 468 (1852). 



2 C. T. Morner, Zeitschr. f. physiol. Chem. 18. 233 (1893). 



3 E. A. Young, Journ. of Physiol. 16. 325 (1894). 



4 C. T. Morner, Zeitschr. f. physiol. Chem. 18. 213 (1893). 



5 E. A. Jernstrom, Holy's Jahresber. f. Tierchem. 1O. 34 (1880). 



