630 PHYSIOLOGICAL CHEMISTRY. 



The nucleoproteins give all the color reactions, are soluble in water con- 

 taining a small quantity of alkali, and are precipitated from this solution by 

 acetic acid. "They are dextro-rotatory. 



(6) Glycoproteins. Compounds of the protein molecule, with a 

 substance or substances containing a carbohydrate group other than a 

 nucleic acid. This carbohydrate group is capable of reducing cupric 

 oxide. Several groups of glycoproteins are differentiated as follows : 



Mucins are secreted by the larger mucous glands of the body, 

 by certain mucous membranes, and are found also in the connective 

 tissue and umbilical cord. The mucins are soluble in water con- 

 taining a little alkali. The solution is mucilaginous, and with acetic 

 acid gives a precipitate insoluble in an excess of the acid. This 

 precipitate is not formed in the presence of 5 to 10 per cent, of 

 sodium chloride. The solution is not coagulated by heat nor pre- 

 cipitated by potassium ferrocyanide. An acid solution containing 

 salts is precipitated by tannic acid, and a similar neutral solution by 

 alcohol, as also by salts of heavy metals. Mucins when pure are 

 acid in reaction, and give the protein color-reactions. 



Mucoids are certain mucin-like substances, such as colloid and 

 ovomucoid, and differing from the mucins in solubility and certain 

 other physical properties. The mucoids are not precipitated by 

 acetic acid. 



Chondroproteins (chondromucoid, amyloid) yield chondroitin- 

 snlphuric acid as one of the decomposition-products. This latter 

 has the power to reduce cupric oxide and to precipitate proteins ; it 

 is sometimes found in the urine. 



Chondromucoid occurs in cartilage; it resembles the mucins in 

 solubility and other properties. 



Amyloid occurs pathologically as an infiltration in the spleen, liver, 

 kidneys, and other organs. Amyloid is insoluble without decomposi- 

 tion. It gives the biuret, xanthoproteic, Millon's, and Adamkiewicz's 

 reactions. 



The reactions with the following coloring-matters are characteristic for 

 amyloid : It is colored red by aniline-green ; also red by methyl-aniline iodide, 

 especially after the addition of acetic acid ; violet or blue by iodine and sul- 

 phuric acid ; and reddish-brown or violet by iodine. 



(c) Phosphoprotein. Compounds of the protein molecule with 

 some, as yet undefined, phosphorus-containing substance other than 

 a nucleic acid or lecithin. Caseinogen, the principal protein con- 

 stituent of milk, belongs to this group. 



