48 THE ALBUMINS. 



magnesium sulphate they are completely precipitated ; with sodium 

 chloride only in part. For ammonium sulphate the limits are 2.9 

 and 4.6. It will thus be noted that as a class the globulins can be 

 readily separated from the albumins by half-saturation with ammo- 

 nium sulphate. Immediately after precipitation by the various 

 methods indicated the globulins are still soluble in dilute saline 

 solution ; but it is noteworthy that after a while they tend to lose 

 their solubility and become coagulated (denaturized) ; this also 

 occurs when they are long kept under water. A number of the 

 globulins show an acid reaction. 



Like the albumins, the globulins are coagulated by heat ; and on 

 hydrolysis, qualitatively at least, they yield the same end-products. 

 Their sulphur content is less than that of the albumins, but not less 

 than 1 per cent. 



Certain members of the group are apparently much more highly 

 differentiated than serum-albumin (lactoglobulin, ovoglobulin, 

 thyreoglobulin, edestin). 



The Gluco -albumins. These comprise the mucins and mu- 

 coids, the most notable members of which are the metalbumin 

 and paralbumin of ovarian cysts (pseudomucin), the mucin of snails, 

 submaxillary mucin, the mucin of frogs' eggs, and of sputum, the 

 mucoid of tendon and of the umbilical cord, the chondromucoid and 

 ovimucoid, etc. These bodies are usually described in text-books 

 under a subdivision of the proteids, viz., as glucoproteids. Their con- 

 sideration under that heading was based on the assumption that they 

 represented compound albumins, resulting from the union of an 

 albuminous radicle with a special carbohydrate group. Since more 

 recent investigation has shown that this group is probably repre- 

 sented in all albumins as well, and is merely present in the " gluco- 

 proteids " in especially large amount, there seems to be no adequate 

 reason for separating them from the albumins proper. It must be 

 added, however, that a carbohydrate group has thus far been 

 demonstrated satisfactorily only in the mucins and mucoids. If 

 present in the other albumins., the amount is certainly very small and 

 totally insufficient to serve as the direct source of the large quanti- 

 ties of sugar which in certain cases of diabetes are known to be 

 derived from the albumins. 



The carbohydrate radicle in question is in most members of the 

 group obtained in the form of chitosamin (glucosamin), which in turn 

 probably exists in the intact molecule as a polysaccharide (FrankePs 

 albamin, for example, see page 45). The structure of this complex 

 mother-substance is but little known, and it appears that in different 

 members of the group it may be different. In the case of the 

 mucins and mucoids Miiller always obtained the chitosamin in 

 association with acetic acid, which suggests that the mother sub- 

 stance might possibly be an acetylated polysaccharide. Other 

 gluco-albumins, such as chondromucin, apparently contain even more 

 complex carbohydrate groups, which yield glucuronic acid besides 



