214 ELEMENTARY PHYSIOLOGY less. 



hepatic cells by the blood : hence the secretion of the 

 bile constitutes a loss to the blood. 



The total quantity of bile secreted in the twenty-four 

 hours varies, but probaljly amounts to not less than from 

 two to three pounds. It is a golden yellow, slightly 

 alkaline fluid, of extremely bitter taste, ccmsisting of 

 water with from 15 per cent, to half that quantity of 

 solid matter in solution. We shall deal with the com- 

 position of bile and tlie nature of its constituents when 

 we come to speak of it in connection with digestion. 

 For the present we may say that its colour is due to 

 bile-pigments ; that it contains certain compounds of 

 sodium with organic acids called bile-salts ; a remark- 

 able crystalline substance called cholesterin ; and 

 some inorganic salts. 



Of these constituents of the bile the essential sub- 

 stances, the bile acids and the colouring matter, ai-e not 

 discoverable in blood which enters the liver ; they must 

 therefore be formed in the hepatic cells. How they are 

 exactly formed we do not at present clearly know. The 

 material of which they are composed is brought to the 

 hepatjp cells by the blood, but the exact condition of 

 that material — whether, for instance, the blood brings 

 something very like the bile acids, and only needing a 

 slight change to be converted into bile acids ; or whether 

 the hepatic cells manufacture the bile acids from the be- 

 ginning, as it were, out of the common material which 

 the blood brings to the liver as to all other tissues and 

 organs — is not as yet quite determined. There is how- 

 ever but little doubt that the pigment of bile is in some 

 way made out of the hremoglobin of the red blood-cor- 

 puscles. The saline matters and cholesterin, on the 

 other hand, aj)pear to be present in the blood of the 

 portal vein, and may therefore, like the water, be simply 

 taken up by the cells from the blood, and passed on to 

 the bile ducts. 



Thus the bile is a continual loss to the blood. But, 



