398 PEACTICAL PHYSIOLOGY 



Besides these, bile also contains traces of soaps, fats and urea. 

 Compounds of glycuronie acid have also been found in bile. The 

 daily secretion amounts to about 750 c.c. To study the chemistry of 

 bile we employ that of the ox, since this is easily procurable. 



EXPERIMENT I. Examine some ox bile. Note that it has a greenish 

 colour, a peculiar musk-like odour, a bitter-sweet taste, a faint alkaline 

 reaction to litmus paper, and that it is of a slimy consistency. 



EXPERIMENT II. If a few drops of weak acetic acid be added to a 

 few cubic centimetres of bile, a stringy precipitate is produced. This 

 consists, in certain animals (ox) of nucleo-protein, in others (man) of 

 mucin. Filter off this precipitate, and note that the filtrate has lost 

 its slimy character. Boil the filtrate ; no coagulum is produced, there- 

 fore bile contains no native protein. 



The above proteins are not produced by the hepatic cells, but are 

 added to the bile in its passage along the bile ducts, being secreted by 

 the mucous lining of these. 



So far as can at present be ascertained, the amounts of pigment and 

 of bile salts do not bear a quantitative relationship to one another, so 

 that it is improbable that they are both derived from the same source. 

 Quantitative estimations of these two bodies in bile, obtained from a 

 biliary fistula, are, however, far from numerous, partly on account of 

 the rarity of suitable cases, and partly because there is no accurate 

 method for quantitatively determining the pigment. 



EXPERIMENT III. Test another portion of the bile for bile salts 

 by PettenJcofer's reaction. To do this place a drop of bile in a small 

 evaporating dish, and move this about so that a thin film of the bile is 

 produced. Now add to the film a very small drop of a concentrated 

 watery solution of cane sugar, and then a few drops of concentrated 

 sulphuric acid. A purple colour is produced, which can be intensified 

 by warming. This pigment shows absorption bands in the spectrum. 

 The chemistry of this reaction is that the sulphuric acid acts on the 

 cane sugar to produce a body called furfuraldehyde, which then reacts 

 with the cholalic acid of the bile salts to produce the pigment. Where 

 only traces of bile salts are present, the test may be made more delicate 

 by using a solution of furfuraldehyde (1 in 1000) instead of cane sugar. 



EXPERIMENT IV. Matthew Hay's Sulphur Test. If a small pinch of 

 powdered sulphur be sprinkled on the surface of bile, or of a solution 

 containing bile salts, it will sink to the bottom of the vessel ; whereas 

 with most other fluids it remains floating on the surface. This reaction 

 depends on the fact that bile salts lower the surface tension of fluids 

 in which they are dissolved. For comparison repeat this test with 

 water. 



