376 MUCUS. 



altogether the case, the separation of the soluble albumen from the 

 insoluble mucin might be very easily effected ; but this is by no 

 means the case, for the swollen, gelatinous, or apparently coagulated 

 mucin only gives up the albumen to the water with difficulty, and 

 after a long time. Hence it is necessary, if we would desire to 

 attain a comparatively successful result, to distribute the mucus 

 repeatedly in water, and after suffering it to form a deposit, to pour 

 only the clear fluid upon the filter, repeating the process until the 

 filtered fluid no longer exhibits any opalescence on heating ; for 

 the insoluble mucous residue cannot be collected on the filter until 

 the albumen has been completely removed. The quantity of the 

 latter substance may be determined by the ordinary rules, and a 

 further separation of the mucin from the epithelium may then be 

 effected by means of diluted alkalies. 



If the substance named pyin occur in the mucus, or if the 

 latter contain a substance not coagulable by heat, but precipitable 

 by acetic acid, although not again soluble in an excess of this acid, 

 the albumen, in case the fluid was not alkaline, must previously be 

 precipitated by boiling, and its quantity determined, after which 

 the pyin-like substance may be separated from the filtered fluid 

 by acetic acid. In case, however, the mucous fluid is alkaline, this 

 substance must first be precipitated by acetic acid, and then washed 

 for some time, in order to remove any albumen that may have been 

 precipitated from the solution by acetic acid ; and after the filtered 

 fluid has been carefully neutralised by ammonia, which generally 

 imparts some degree of turbidity to it, it must finally be boiled. 



The quantitative determination of the remaining organic and 

 mineral constituents of the mucus may easily be conducted by 

 following the rules already given. 



We are necessarily unable to form any estimate of the quantity 

 of mucus secreted by the different mucous membranes ; and it 

 would seem sufficient to draw attention to the view advanced by 

 Valentin, that the secretion separated from the surface of many of 

 the mucous membranes must be regarded as exceedingly small, or 

 even absolutely nothing in the normal state. It can only be re- 

 garded as the result of special or general irritation, when any con- 

 siderable quantity of mucus is separated from an apparently 

 healthy mucous membrane ; a view which seems to derive con- 

 firmation from the circumstance, that normal mucus can never be 

 obtained from the living body in quantities sufficient for chemical 

 analysis, but must be scraped away from the mucous membrane of 

 animals immediately after they have been killed. The liability to 



