21 



umbilical cord. Mucin gives the proteid color reactions, and 

 forms a mucilaginous solution with water containing- a little 

 alkali. This solution is not coagulated by heat, but forms a 

 precipitate with acetic acid insoluble in an excess of acid. 



Mucoids include colloid and ovamucoid. They occur in 

 the organism and differ from mucins in physical properties and 

 solubility, and are not precipitated by acetic acid. 



Chondroproteids yield on hydrolysis chondroitin, sulphuric 

 acid, and an ethereal sulphuric acid in combination with a 

 carbohydrate. This acid and nucleic acid have the power of 

 forming with proteids a compound precipitated by acetic acid, 

 which is occasionally found in the urine, and is called nucleo- 

 albumin. Important chondroproteids are chondromucoid, 

 found in cartilage, and amyloid, found in various organs path- 

 ologically. 



28. Nucleoproteids, on hydrolysis, yield nucleins. Three 

 varieties are known, differing in hydrolytic products. 



(1). Cell-Nucleins yield a proteid, ortho-phosphoric acid, 

 and xanthin bases, and occur chiefly in the nuclei of cells, but 

 also in the protoplasm, and may pass into the animal fluids 

 when the cell is destroyed. 



(2). Pseudonucleins yield proteid and ortho-phosphoric 

 acid, and occur in almost all animals and vegetables. Casein 

 of milk is a nucleoproteid containing a pseudonuclein. 



(3). Nucleic acid yields ortho-phosphoric acid and xan- 

 thin bases, and occurs in the nuclei of the spermatozoa alone. 



All give the proteid color reactions, are soluble in water 

 containing a little alkali, and are precipitated from this solu- 

 tion by acetic acid. Nucleins are not decomposed by gastric 

 juice, and are obtained as an insoluble residue after the arti- 

 ficial digestion of nucleoproteids with pepsin. 



29. Albuminoids. Albuminoids are a group of proteins 

 whose general properties suggest them to be anomalous simple 

 proteids. They consist of a number of bodies which, in their 

 general characters and elementary composition resemble pro- 

 teids, but differ from them in many respects. They are amor- 

 phous. Some of them contain sulphur, and others do not.'^ 

 The decomposition-products resemble the decomposition-pro- 

 ducts of proteids. 



