FAECES. 371 



tion of an acid a bright red deposit is formed. On adding a 

 little tannic acid it is precipitated in the form of a red powder, 

 and by an excess of that reagent, in greyish-brown flocculi. 



The substance (A) which is soluble in water but not in al- 

 cohol, consists of albumen coloured brown by bile, containing, 

 mixed with it, alkaline sulphates and phosphates, and phosphate 

 of lime. 



That portion of the faeces which is insoluble in water, and 

 remains floating on its surface, consists of a mixture of intes- 

 tinal mucus and of the substances precipitated by the bile : it 

 is very viscid, clogs up the pores of filtering paper, and dries 

 upon it as a glistening, brittle, and elastic coating ; on being 

 again placed in water it softens, and, especially if any free alkali 

 is present, becomes viscid as before. 



This mass is perfectly soluble in caustic potash, and may 

 be again thrown down by the addition of an acid ; the fluid 

 then gives off an odour of bile. Ether and alcohol take up fat 

 and biliary resin, and yield greenish extracts. The ethereal 

 solution becomes turbid on the addition of alcohol in conse- 

 quence of the precipitation of fat ; the residue left after eva- 

 poration melts in boiling water, leaves spots of fat on filtering 

 paper, and dissolves in caustic potash; hence it contains no 

 cholesterin. The portion left after the aforesaid extractions 

 with ether and alcohol, imparts to water a peculiar yellow 

 matter, which soon changes to a darker tint after exposure 

 to the air ; it is devoid of odour or taste, and rapidly becomes 

 putrid. It is at first insoluble in alcohol, but it becomes soluble 

 as decay commences ; moreover when fresh it is hardly rendered 

 turbid by the addition of infusion of galls, but is strongly precipi- 

 tated by that reagent after the commencement of putrefaction. 

 If this substance, when quite fresh, is mixed with the solution 

 of fat and biliary resin which we have just described, we observe 

 a grayish-green precipitate which deposits itself as slowly as the 

 precipitate from which these substances were originally obtained. 

 Hence, as Berzelius remarks, we may conclude that the excre- 

 ments contain an insoluble combination of the constituents of 

 the bile, with other materials which have been added to it in 

 the course of the digestive process. 



The analysis of human faeces, sufficiently consistent to form 



