254 



DIGESTION 



nascent hydrogen, is reduced to hydrolilirubin C 82 H 40 N 4 O 7 which also occurs at 

 times in the human bile. Since bilirubin and biliverdin are commonly present 

 together in the bile, the color of the fluid is somewhere between red and green, 

 and varies toward one or the other according as one pigment or the other pre- 

 dominates. 



The bile contains also mucin, cholesterin, jecorin, lecithin, neutral fats and 

 soaps, ethereal sulphuric acids, paired glycuronic acids, cholin, glycerin-phos- 

 phoric acid (both the latter, decomposition products of lecithin), and various 

 mineral constituents, namely: the alkalies in combination with the bile acids, 

 sodium chloride, potassium chloride, calcium and magnesium phosphate and 

 iron. Sulphates occur, if at all, in very small quantities. A diastatic and a 

 fibrin-splitting ferment have been demonstrated in the bile of certain animals; 

 but it is not quite certain that they are formed in the liver, for they might rep- 

 resent enzymes only reabsorbed into the bile. 



The following summary of analytical results with regard to the quantita- 

 tive composition of bile may be given : 



The chief importance of bile in digestion appears to be that, in virtue 

 of its bile salts it has the power to dissolve the free fatty acids and to increase 

 the solubility of soaps ; but more on this under the subject of absorption from 

 the intestine. 



Proof that the bile pigments are formed for the most part in the liver is 

 found in the fact that when this organ is extirpated from birds, or when all 

 the blood vessels of the liver and the bile ducts are ligated, not a trace of bile 

 pigments can be demonstrated anywhere in the animal. 



The bile pigments are universally regarded as derivatives of haemoglobin. 

 The following facts among others speak for this view. A pigment called hcemo- 

 toidin found in old blood stains is closely related to bilirubin and probably is 

 identical with it. Hcematinic acid, C 8 H 9 NO 4 , which is the first oxidation product 

 of hcematin when oxidation takes place at the lowest possible temperature, appears 

 to be identical with biliverdinic acid, an oxidation product of bilirubin (Kiis- 

 ter). When dissolved hemoglobin is injected into the blood, or when substances 

 which liberate haemoglobin from the corpuscles are taken into the body, the quan- 

 tity of pigments excreted in the bile increases materially. 



Since it has been shown in these and other researches that the secretion of 

 bile pigments never runs parallel to that of the bile acids, it follows that these 

 two chief constituents are not derivatives of the same substance. 



