448 EXCRETION. 



into hot water, or steaming it, taking care that it be carefully wiped. We now have the 

 cholesterine mixed with a certain quantity of saponifiable fat. After the fluid has evapo- 

 rated, we can see the cholesterine crystallized in the watch-glass, mingled with masses 

 of fat. This we remove by saponification with an alkali ; and, for this purpose, we add 

 a moderately strong solution of caustic potash, which we allow to remain in contact 

 with the residue for one or two hours. If much fat be present, it is best to heat the 

 mixture to a temperature a little below the boiling-point ; but in analyses of the blood 

 this is not necessary. The mixture is then to be largely diluted with distilled water, 

 thrown upon a small filter, and thoroughly washed till the fluid which passes through is 

 neutral. We then dry the filter and fill it up with ether, which, in passing through, 

 dissolves out the cholesterine. The ether is then evaporated, the residue extracted with 

 boiling alcohol as before, the alcohol collected on a watch-glass previously weighed, and 

 allowed to evaporate. The residue consists of pure cholesterine, the quantity of which 

 may be estimated by weight. 



The accuracy of this process may be tested by means of the microscope ; for the crys- 

 tals have so distinctive a form that it is easy to determine, by examining the watch-glass, 

 that the cholesterine is perfectly pure. In making this analysis quantitatively, it is 

 necessary to be very careful in all the manipulations ; and, for determining the weight of 

 such minute quantities, an accurate and delicate balance, one, at least, that will turn with 

 the thousandth of a gramme, carefully adjusted, must be employed. With these precau- 

 tions, the quantity of cholesterine in any fluid or solid may be determined with perfect 

 accuracy ; and the estimate may be made in a quantity of blood not exceeding fifteen or 

 twenty grains. In analyzing the brain and bile, we found it necessary to pass the first 

 ethereal solution through animal charcoal, in order to get rid of the coloring matter. 

 In doing this, the charcoal must be washed with fresh ether until the solution which 

 passes through is brought up to the original quantity. The other manipulations are the 

 same as in the analyses of the blood. In examining the meconium, we found that the 

 cholesterine which crystallized from the first alcoholic extract was so pure that it was 

 not necessary to subject it to the action of an alkali. 



The proportion of cholesterine in the bile is not very large. In the table, it is esti- 

 mated at from 0'62 to 2*66 parts per thousand. In a single examination of the human 

 bile, we found the proportion 0*618 of a part per thousand. 



The origin and destination of this principle involve, as we believe, an office of the 

 liver which has not hitherto been recognized by physiologists; and we shall consider 

 these questions specially, under the head of the excretory function of the liver. 



Itiliverdine. The coloring matter of the bile bears a certain resemblance to the color- 

 ing matter of the blood and is supposed to be formed from it in the liver. It gives 

 to the bile its peculiar tint, and has, as we have remarked, the property of coloring 

 the tissues with which it comes in contact. Whenever the flow of bile is seriously 

 obstructed, the coloring matter is absorbed by the blood, and it can be readily detected 

 in the serum and in the urine. It also colors the skin and the conjunctiva. In the bile 

 it is liquid, but it may be coagulated and extracted by various processes. It does not 

 exist naturally in the form of pigmentary granulations. 



This principle is precipitated from the bile by boiling with milk of lime. The filtered 

 residue is then decomposed with hydrochloric acid, which unites with the lime and leaves 

 a fatty residue, of an intense-green color. The fat is then removed by repeated washings 

 with ether, which is a very long and difficult process. The precipitate is then redissolved 

 in alcohol with ether added, which gives to the liquid a bluish-green color, and leaves, 

 after evaporation, a dark-green powder. This powder contains iron, but its proportion 

 has never been accurately estimated. The matter thus obtained is insoluble in water and 

 in chloroform, but it is soluble in ether, alcohol, sulphuric and hydrochloric acid. 



It is unnecessary to follow out in detail all of the chemical investigations which have 



