28 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



neutral salts as sodium chloride and magnesium sulphate. If dis- 

 solved in acid or alkali, they are not coagulated by heat. 



A variety of alkali albumin (probably a compound containing a 

 large quantity of alkali) may be formed by adding strong potash to 

 undiluted white of egg. The resulting jelly is called Lieberkiihn's 

 jelly. A similar jelly is formed by adding strong acetic acid to un- 

 diluted egg-white. 



The halogens (chlorine, bromine, and iodine) also form albumi- 

 nates, and may be used for the precipitation of proteids. 



B. The Compound Proteids 



The compound proteids are compounds of albuminous substances 

 with other organic materials, which are as a rule also of complex 

 nature. 



They may be divided into the following groups : — 



1. Haemoglobin and its aUies. These are compounds of proteid 

 with an iron-containing pigment, and will be fully considered under 

 Blood. 



2. Gluco-proteids. These are compounds of proteids with members 

 of the carbohydrate group. This class includes the mucins, and 

 substances allied to the mucins, called mucoids. 



Dr. Pavy has shown that a small quantity of a similar carbo- 

 hydrate can be spUt off from various other proteids, which we have 

 already classified as simple proteids. 



Mucin is a widely distributed substance, occurring in epithehal 

 cells, or shed out by them (mucus, mucous glands, goblet cells) ; and 

 in connective tissue where it forms the chief constituent of the 

 ground substance or intercellular material. 



The mucin obtained from different sources varies in composition 

 and reactions. There are probably several mucins ; they all agree 

 in the following points : — 



(a) Physical character. Viscid and tenacious. 



{b) Precipitability from solutions by acetic acid ; they all dissolve 

 in dilute alkalis like lime water. 



{c) They are all compounds of a proteid with a carbohydrate 

 provisionally called animal gum, which by treatment with dilute 

 mineral acid can be hydrated into a reducing but non-fermentable 

 sugar, the nature of which is at present uncertain. 



The mucoids differ from the mucins either in being non-precipitable 

 from alkaline solutions by acetic acid, or in being readily soluble in 

 excess of acetic acid. One of these, called ovo-miicoid, is found in 



