THE PRO TEWS. 45 



subgroups differ from each other in many respects, and the differ- 

 ent representatives of each group, moreover, possess certain features 

 Avhich serve to distinguish them from each other. 



The mucins proper, which include the mucin that is furnished by 

 the large mucinous glands, the mucin that is found in tendons and 

 the umbilical cord, that which is secreted by snails, and that found 

 in the capsule of frogs' eggs, are insoluble in water. They possess 

 acid properties, and dissolve in water after neutralization with an 

 alkali. Such solutions do not coagulate on heating, but are precip- 

 itated on acidifying with acetic acid. This precipitate is insoluble 

 in an excess of the acid. In the presence of from 5 to 10 per cent, 

 of sodium chloride, however, they are not precipitated in this 

 manner. From such acid solutions they are not thrown down by 

 potassium ferrocyanide, while tannic acid causes the rnucin to sepa- 

 rate out. Neutral solutions of the mucins are precipitated by 

 alcohol in the presence of neutral salts. Similar results are ob- 

 tained with some of the salts of the heavy metals. When heated 

 on a water-bath with dilute hydrochloric acid (2 per cent.) the 

 mucins are decomposed, with liberation of the carbohydrate group, 

 which can be demonstrated with Fehling's test (see Urine). Ac- 

 cording to more modern investigations, however, it appears that the 

 radicle which is thus split off is not a true carbohydrate. Miiller 

 and Seemann were thus able to isolate a crystalline substance from 

 mucins which was apparently identical with glucosamin, and Leathes 

 obtained a body which he regards as a reduced chondrosin. Levene 

 concludes from his recent investigations that the mucins contain the 

 complex of chondroitin-sulphuric acid. This would account in a 

 satisfactory manner for the acid properties of the mucins, and the 

 fact that they yield a reducing-substance on decomposition. This, 

 however, is not a carbohydrate proper, but glucosamin. 



All mucinous solutions are more or less viscid, and are therefore 

 extremely difficult to filter. In the dry state they are a white or 

 yellowish-gray powder. 



The mucoids, or mucinoids, are found in the cornea and the 

 vitreous humor of the eye, in the white portion of birds' eggs, in 

 cartilage, and are very abundant in certain ovarian cysts, where two 

 distinct varieties have been encountered, viz., the so-called metalbu- 

 min or paralbumin, or pseudomucin, and colloid. They will be con- 

 sidered in detail later. 



The hyalogens comprise a class of substances which, according to 

 Krukenberg, are essentially characterized by the fact that on treat- 

 ment with alkalies they are decomposed into an albuminous sub- 

 stance and into nitrogenous carbohydrate-like bodies, the so-called 

 hyalinSj which in turn are said to yield a carbohydrate proper on 

 further decomposition. 



Among the hyalogens may be mentioned the neossin which is 

 found in edible Chinese swallow nests ; membran in, obtained from 

 Descemet's membrane and the capsule of the crystalline lens ; 



