372 MUCUS. 



separated by filtration from the morphological substances. The 

 mucous juice does not coagulate when exposed to heat, but 

 becomes in some instances more thinly fluid and more nearly 

 similar to a true solution. Alcohol precipitates the mucin from 

 the fluid in flakes and threads, while dilute acetic acid pre- 

 cipitates it in the form of viscid flakes ; if it occurs as a gelatinous 

 mass, it is converted by the same acid into white threads or fibres. 

 The flakes and fibres are insoluble in extremely dilute acetic acid, 

 but they dissolve when treated with the concentrated acid and with 

 the aid of heat. The mineral acids behave in a similar manner, 

 precipitating the mucin when diluted, and again dissolving it 

 very readily when employed in a concentrated state. Mucin, on 

 the other hand, dissolves very readily in dilute alkalies, but much 

 less speedily in concentrated solutions. Acetic acid precipitates a 

 larger quantity from dilute than from concentrated alkaline solu- 

 tions, which is owing to the circumstance, that mucin, if not 

 entirely soluble, yet admits of being reduced to a gelatinous state 

 in solutions of alkaline salts, when not too dilute. Acetate of 

 potash prevents the mucin in these cases from separating perfectly 

 into flakes. Gelatinous mucus is frequently, as it were, coagulated 

 by water, which causes it to become denser, and to lose its trans- 

 lucent, gelatinous character. This change is very probably owing 

 to the abstraction by the water of the alkali or alkaline salts to 

 which it partially owes this gelatinous condition. Ferrocyanide 

 of potassium does not throw down mucin from the alkaline or the 

 acid solution. (When, as is frequently the case, the mucus is 

 precipitated from the acetic-acid solution by ferrocyanide of 

 potassium, albumen or some similar protein-body is probably 

 present with the mucin.) When, on the other hand, mucus 

 is boiled with concentrated acetic acid, it will be very copiously 

 precipitated by ferrocyanide -of potassium. Hot concentrated 

 nitric acid colours it yellow, while it is changed to a blue colour 

 when heated with hydrochloric acid and exposed to the air. 

 Tannic acid or basic acetate of lead gives rise to a considerable 

 precipitate from the aqueous, weak alkaline mucous solution, whilst 

 nothing beyond a faint turbidity is induced by alum, chromic acid, 

 bichloride of mercury, neutral acetate of lead, and other metallic salts. 

 Several elementary analyses of mucus have been instituted, 

 but they can scarcely afford us any aid in judging of the compo- 

 sition of the mucin, since the epithelium has been included in the 

 substance examined. Scherer, who has alone succeeded to some, 

 extent in exhibiting a preparation in any degree fit for an 



