THE PROTEIN SUBSTANCES. 33 



caustic alkali solution, as a 5 per cent KOH solution, is allowed to 

 act on sub-maxillaris mucin, we obtain alkali albuminate, a body 

 similar to albumose and peptone, and one or more substances of an 

 acid reaction and with strong reducing powers. 



In one or the other respect the different mucins act somewhat 

 differently. For example, the snail and nerve mucins are insoluble 

 in dilute hydrochloric acid of 1-2 p. m., while the mucin of the 

 submaxillary gland and the navel cord are soluble. Nerve-mucin 

 becomes flaky with acetic acid, while the other mucins are precipi- 

 tated in more or less fibrous, tough masses. Still all the mucins 

 have certain reactions in common. 



In the dry state mucin forms a white or yellowish-gray powder. 

 When moist it forms, on the contrary, flakes or yellowish-white 

 tough lumps or masses. The mucins are acid in reaction. They 

 give the color reactions of the albuminous bodies. They are not 

 soluble in water, but may give a neutral solution with water and 

 the smallest quantity of alkali. Such a solution does not coagulate 

 on boiling, while acetic acid gives at the normal temperature a 

 precipitate which is insoluble in an excess of the precipitant. If 

 5-10$ NaCl be added to a mucin solution, this can now be care- 

 fully acidified with acetic acid without giving a precipitate. Such 

 acidified solutions are copiously precipitated by tannic acid; with 

 potassium ferrocyanide they give no precipitate, but on sufficient 

 concentration they become thick or viscous. A neutral solution of 

 mucinalkali is precipitated by alcohol in the presence of neutral 

 salts; they also give precipitates with several metallic salts. If 

 mucin is heated on the water-bath with dilute hydrochloric acid of 

 about 2$, the liquid gradually becomes a yellowish or dark brown 

 and reduces copper oxhydrate from alkaline solutions. 



The mucin most easily obtained in large quantities is the sub- 

 maxillary mucin, which may be prepared in the following way: 

 The filtered watery extract of the gland, as colorless as possible, is 

 treated with 25$ hydrochloric acid, so that the liquid contains 

 1.5 p. m. HC1. On the addition of the acid the mucin is imme- 

 diately precipitated, but dissolves on stirring. If this acid liquid is 

 immediately diluted with 2-3 vols. of water, the mucin separates 

 and may be purified by redissolving in 1-5 p. m. acid and diluting 

 with water and washing therewith. The mucin of the navel-cord 



