THE METHOD OF ANALYSING IT. 375 



formed solely from the constituents of the blood-plasma. I know 

 of only one analysis of the kind suited to throw light on the sub- 

 ject, and this yielded more potash and less soda in the ash of the 

 mucus than in that of the blood-serum ; but as this mucus had 

 been secreted during an acute catarrh, and besides being very rich 

 in young cells (mucus-corpuscles), contained also some granular 

 cells, it does not afford any conclusive evidence. 



The method of analysing mucus would be very simple, if it 

 were not wholly impracticable, in most cases, to separate the true 

 mucin from the cells which are intermixed with it. It is only in 

 a few rare instances, as in the case investigated by Scherer, and 

 already referred to, that the morphological elements can be col- 

 lected on the filter by mixing the object with a large quantity of 

 water, and rendering it capable of being filtered by repeated and 

 continuous shaking. The mucin, however, instead of being distri- 

 buted through the water, is in many instances converted into an 

 apparently coagulated condition, this being more especially the 

 case with catarrhal bronchial mucus, which becomes shrunk by the 

 abstraction of the alkaline salts whichhad previously caused the mucus 

 to present a swollen appearance. When the mucin is not soluble 

 in water, the only method of determining it even in an approximate 

 degree, is to filter the substance after it has been digested with 

 highly diluted ammonia. Unfortunately, however, the mucin which 

 has been dissolved by the alkali passes very slowly through the 

 filter, in consequence of the obstruction presented by the gelatinous 

 swollen epithelium. In many cases, therefore, this method proves 

 insufficient for the separation of the mucin from the above described 

 morphological elements. If we succeed in removing the epithelium 

 by filtration, the mucin may be precipitated from the neutral or 

 weakly acid solution by spirit, and from the alkaline solution by 

 dilute acetic acid ; after this, the precipitate must be washed with 

 hot spirit, and after being dried at a temperature of 120, must 

 again be washed with hot water, in order to remove all the mineral 

 and organic substances which are insoluble "in spirit. The waters 

 employed in rinsing must then each be strongly concentrated, and 

 immediately evaporated with the spirituous solution filtered off 

 from the mucin, while the residue is extracted with ether, alcohol, 

 and water. 



When albumen is present with the mucin, which indeed it very 

 generally is in the large quantities of the substance necessary for 

 such investigations, the difficulty of the analysis is greatly increased. 

 If the mucin were insoluble in water, which appears to be never 



