260 EXCRETION. 



small quantity of this coloring matter finds its way into the 

 circulation. 



Perfectly normal and fresh bile, examined with the micro- 

 scope, presents only a certain amount of mucus, the charac- 

 ters of which we have already described. There are no 

 formed anatomical elements characteristic of this fluid. The 

 fatty and coloring matters are in solution, and not in the 

 form of globules or granules. 



Composition of the Bile. 



It is a remarkable fact, that although the bile, in a per- 

 fectly fresh and normal condition, may be obtained from the 

 inferior animals with the greatest facility, no satisfactory 

 analyses of its characteristic principles were made before the 

 examinations of ox-gall by Strecker, in 1848. The bile is, 

 however, one of the most important, but least understood, 

 of the animal fluids ; and our scanty information with regard 

 to its functions has been in a measure due to the want of an 

 exact knowledge of its physiological chemistry. We shall 

 study the composition of the bile very closely, and shall show 

 that it contains two classes of constituents ; one class ele- 

 ments of secretion which is reabsorbed ; and another an 

 element of excretion which is discharged in a modified form 

 in the faeces. The latter involves a newly-described function 

 of the liver, but our information is much more positive and 

 definite concerning it than with regard to the digestive action 

 of the bile. In treating of the subject of digestion, we have 

 already indicated some of the difficulties, which have been 

 but imperfectly overcome, in the study of the action of the 

 bile as a true secretion, or a recrementitious fluid. The rea- 

 son why the same obscurity has prevailed, until very recently, 

 with regard to the function of the bile as an excretion is 

 that physiologists have regarded what are known as the 

 biliary salts as the only really important constituents ; and 

 these salts have eluded chemical investigation after the dis- 

 charge of the bile into the small intestine. Our recent posi- 



