CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 355 



herbivorous animals, a yellowish green, or a bright green, or a 

 dirty green, according to circumstances, being much modified by 

 retention in the gall-bladder. The reaction is neutral or alkaline. 

 The following may be taken as the average composition of human 

 bile taken from the gall-bladder, and therefore containing much 

 more mucus as well as, relatively to the solids, more water than 

 bile from the hepatic duct. 



In 1000 parts. 



Water 859'2 



Solids : 



Bile Salts 914 



Fats, &c 9-2 



Cholesterin 2*6 



Mucus and Pigment 29'8 



Inorganic Salts 7*8 



140-8 



The entire absence of proteids is a marked feature of bile ; pan- 

 creatic juice, as we shall see, contains a considerable quantity, 

 saliva, as we have seen, a small quantity, normal gastric juice 

 probably still less and bile none at all. Even the bile which has 

 been retained some time in the gall-bladder, though rich in mucus, 

 contains no proteids. 



The constituents which form, apart from the mucus, the great 

 bulk of the solids of bile and which deserve chief attention, are 

 the pigments and the bile-salts; of these we shall speak im- 

 mediately. 



With regard to the inorganic salts actually present as such 

 sodium salts are conspicuous, sodium chloride amounting to -2 or 

 more per cent., sodium phosphate to nearly as much, the rest 

 being earthy phosphates anct other matters in small quantity. The 

 presence of iron, to the extent of about *006 p.c., is interesting, 

 since, as we shall see, there are reasons for thinking that the pig- 

 ment of bile, itself free from iron, is derived from iron-holding 

 haemoglobin ; some, at least, of the iron set free during the con- 

 version of haemoglobin into bile pigment, which probably takes 

 place in the liver, finds its way into the bile. Bile also appears 

 to contain a small quantity, at all events occasionally, of other 

 metals, such as manganese and copper ; metals introduced into the 

 body are apt to be retained in the liver and eventually leave it by 

 the bile. 



The small quantity of fat present consists in part of the com- 

 plex body lecithin. 



The peculiar body cholesterin, which though fatty looking 

 (hence the name ' bile fat ' ) is really an alcohol with the composi- 

 tion CseH^O, is conspicuous by its quantity and constancy. It 

 forms the greater part of most gall-stones, though some are com- 

 posed chiefly of pigment. Insoluble in water and cold alcohol, 



