400 PRACTICAL PHYSIOLOGY 



sulphuric acid down the side of the tube so as to form a layer underneath the 

 watery solution. A violet ring is formed where the two fluids meet. Now place 

 the test tube in a beaker of cold water, and shake gently so as to mix the two 

 fluids. A violet solution is thus obtained. (By cooling the test tube in water too 

 great a rise of temperature is avoided). Divide the violet solution into two parts, 

 A and B. Add A to some ether and examine by means of the spectroscope a 

 distinct band is seen in the green. Add B to some absolute alcohol and note that, 

 although the spectrum is at first the same as in A, a band gradually develops in 

 the blue, and that, along with the development of this, the tint of the solution 

 changes from violet to brown. 



ADVANCED EXPERIMENT. To Prepare Pure Glycocholic Acid. In certain 

 districts of Germany and America it has been observed that the glycocholic acid 

 can be separated from the bile by a very simple process, and, so far as it has as 

 yet been tried, the bile obtained from oxen reared in this country appears to be 

 suitable for the process. The method is as follows : 



Some ox bile is placed in a stoppered cylindrical vessel, and mixed with ether 

 and hydrochloric acid in the proportion of ten parts of the former and four parts 

 of the latter, for every hundred parts of bile. A few crystals of glycocholic acid 

 are added to the mixture so as to start the crystallisation, the vessel is stoppered, 

 vigorously shaken, and then allowed to stand in a cool place. After some time 

 the mass will be found to be " solid " with crystals. These are collected in a 

 filter paper, and washed with cold distilled water till no more pigment can be 

 removed. They are then removed to a flask and dissolved in boiling water ; the 

 solution is filtered hot, and the filtrate, on cooling, deposits numerous acicular 

 crystals of the acid. These may now be collected, washed with distilled water, 

 and dried (for Chemistry and Reactions, see p. 398). 



Preparation Of Taurin. Bile from carnivorous animals cat or dog is 

 heated on a sand-bath with one-third its bulk of concentrated hydrochloric acid 

 until a resinous-like mass of the anhydride of cholalic acid (called Dyslysin) has 

 formed. This can be drawn out into brittle threads by means of a glass rod. 

 The dyslysin is filtered off, and the filtrate is evaporated to a small bulk, the 

 sodium chloride, which crystallises out during the evaporation, being removed by 

 filtration. The thin syrup is then poured into fifteen times its bulk of alcohol, 

 and left standing twenty-four hours, when the taurin will have crystallised out. 

 It can be purified by collecting the crystals on a filter paper, and washing with 

 cold water. 



The Bile Pigments. These are bilirubin and biliverdin. The 

 former occurs most plentifully in the bile of carnivorous, the latter in 

 that of herbivorous animals. Their presence can be detected by 

 oxidising a mixture containing them with nitrous acid, when a play of 

 colours green, blue, purple, and then yellow is produced. This is 

 called Gmelin's test. 1 



EXPERIMENT V. Dilute some ox bile with an equal amount of 



a This test depends on the various colours of the oxidation products of bili- 

 rubin. The first oxidation product is bili-verdin, which is green ; the next is 

 bili-cyanin, which is blue ; the next is bili-purpurin, which is purple ; and the 

 last is choletelin, which is yellow. 



