CH. II.] MUCIN. 57 



63. Treat 5 cc. of the filtrate from Ex. 62 with two volumes of 

 40 per cent. NaOH and a drop of copper sulphate. A pink colour is 

 formed. 



64. Add a few drops of a solution of tannic acid. A white 

 precipitate is formed. 



65. Add a few drops of a solution of lead acetate. A white 

 precipitate is formed. 



J. The Gluco-proteins. 



These bodies are conjugated proteins, the protein being 

 united to a carbohydrate group. 



They consist of the mucins and mucinoids or mucoids. 

 The mucins are found in connective tissue and are secreted 

 by certain of the salivary glands and various parts of the 

 alimentary canal, notably the large intestine. Their 

 solutions are viscous. They are soluble in dilute alkalies 

 and are precipitated from solution by acetic acid, the 

 precipitate being insoluble in excess of acetic acid. They 

 are also soluble in o-i per cent, hydrochloric acid. On 

 hydrolysis with acids the sugar group is split off and will 

 reduce Fehling's solution. 



The mucoids are not so viscous and not so readily 

 precipitated by acetic acid, the precipitate being soluble 

 in excess. They are found in ovarian cysts and in white of 

 egg [see Ex. 41 (e)]. 



Preparation of Mucin, Mince the submaxillary gland of an ox, grind 

 with sand and add o-i per cent. NaOH (i litre to 50 grams of the moist gland). 

 Shake well in a large bottle from time to time and leave for about half an hour . 

 Strain through muslin and filter through coarse filter-paper. (This crude 

 solution should not be prepared too long before use, as mucin loses its 

 characteristic properties if left standing with alkalies.) 



66. Add acetic acid drop by drop. A stringy precipitate is 

 formed, insoluble in excess of the acid. 



67. Remove the precipitate on a glass rod, wash with water, 

 and apply the usual colour reactions for proteins, e.g. xanthoproteic, 

 glyoxylic, and Millon's. They are all given by mucin. 



