74 THE SECRETIONS: 



in it in a state of solution, as is obvious from microscopic ex- 

 amination. There can, I conceive, be no doubt that the prin- 

 cipal constituent of the fluid, mucin, 1 is held in solution by 

 means of an alkali, since water (by taking up the alkali) is 

 sufiicient to precipitate it, and the effect is produced in a much 

 higher degree by the addition of a free acid. 



When mucus is allowed to remain in contact with water, 

 a slight quantity of the mucin always dissolves, probably through 

 the aid of a free alkali ; hence it is that the water in which the 

 sputa, during catarrhal affections, are allowed to float, always 

 become slightly turbid on the addition of acetic acid. 



In addition to the mucin, the fluid portion of the mucus also 

 contains a small quantity of extractive matters and salts, (espe- 

 cially lactate of soda and chloride of sodium,) and either no 

 albumen, or at any rate a mere trace. The contents of the 

 mucus-corpuscles are not accurately known; in all probability 

 they contain a fluid in addition to their nuclei. The fat that 

 occurs in mucus is probably contained in the corpuscles, for no 

 fat-vesicles are generally observed in fresh mucus, but after the 

 solution of the corpuscles by the addition of acetic acid, a few 

 fat-vesicles make their appearance ; indeed in some of my obser- 

 vations, the nuclei of the mucus- corpuscles, have seemed to lose 

 their dark granular appearance, and, after a time, to become 

 clear and like minute fat-vesicles. The nuclei of mucus-cor- 

 puscles do not appear to undergo this change invariably ; there 

 are probably different stages of development, and on the as- 

 sumption that the nuclei of the least- developed corpuscles are 

 composed of fat, the relative increase of fat will clearly corre- 

 spond with the amount of mucus that is secreted. 



1 [Simon observed the great similarity between mucin and pyin ; the researches 

 of Eichholtz seem to show that these substances are identical. The substance de- 

 scribed by Eichholtz as pyin differs from the protein-compounds in being precipitated 

 from an alkaline solution by an aqueous solution of iodine and by distilled water. A 

 considerable excess of water dissolves a slight portion of it. Dilute mineral acids, when 

 carefully added, precipitate it, but when in slight excess, immediately redissolve it ; 

 moreover, ferrocyanide of potassium causes no precipitate in a clear acid solution, but 

 a turbidity is produced by the same substances that throw it down from its alkaline 

 solutions. Acetic, tartaric, and oxalic acids precipitate, but do not redissolve it, and 

 a solution of alum, gradually added, produces a precipitate insoluble in an excess of the 

 test. On evaporating an alkaline solution of mucin on the water-bath, it becomes 

 covered with a film of coagulated mucin which is difficult of solution in water.] 



