EXCREMENTITIOUS SUBSTANCES. 97 



of the substance is then entirely changed. When the yellow alkaline solution 

 is treated with hydrochloric acid, the pigment is precipitated with a green tint ; 

 this precipitate forms a red solution with nitric acid, and a green solution with 

 the alkalies, and appears to be perfectly identical with the green modification of 

 bile-pigment. When acids are added to fresh bile, a green color is produced, 

 if oxygen be present, but not if it be excluded. Bile-pigment is occasionally 

 found in the urine in large quantities, when its secretion by the natural channel 

 is prevented ; and it may be readily recognized by the nitric acid test. There 

 is much uncertainty in regard to the precise composition of this substance, for 

 the reasons already specified; the analyses which have been made of it, however, 

 indicate that it is remarkable for the enormous proportion of carbon which it 

 contains, this being as much as 68 per cent., and thus exceeding the proportion 

 of that element in the black pigment of the eye, and in abnormal melanic de- 

 posits; it contains also about 8 per cent, of nitrogen. The bile of the Ox 

 contains a green pigment which seems to be distinct from the preceding, not 

 undergoing changes of color when treated with nitric acid, and containing little 

 or no nitrogen ; this was considered by Berzelius to be identical with the chloro- 

 phyll of plants, and was designated by him as biliverdin; it does not seem, 

 however, to be present in human bile. Another pigmentary substance has been 

 discovered in bile, however, which is distinguished by its crystalline form, and 

 by its reddish-yellow hue ; this was named by Berzelius bilifulvin. The source 

 of these coloring matters is probably to be looked for, as already pointed out 

 ( 31), in the hsematin of the red corpuscles ; which undergoes changes, after 

 their disintegration has commenced, that show a decided approximation to them. 

 And it is a most important confirmation of this view, that hsematin, when 

 effused in situations where it can be acted on by the air, exhibits most of the 

 shades of color which have been mentioned as characteristic of biliphaein ; as 

 is seen in the ordinary case of a cutaneous ecchymosis. With regard to the 

 place in which the actual transformation occurs, however, we are entirely igno- 

 rant; for although bile-pigment frequently shows itself in large quantities in the 

 blood, and is deposited by it in the tissues and fluids, saturating the bones, 

 teeth, cartilages, ligaments, fibrous tissues (being especially evident in the scle- 

 rotic coat of the eye, and in the skin), showing itself also in the nerves, the 

 crystalline lens, and the vitreous humor, and more or less tinging all the secre- 

 tions and exudations into which the fluid of the blood passes ; yet this may 

 fairly be attributed, as we shall presently see, to the reabsorption of the pigment 

 subsequently to its elimination by the liver ( 71). And looking to the general 

 physiological relations of this organ, hereafter to be pointed out, we may surmise, 

 without improbability, that it is by its agency that the transformation is effected, 

 and that the bile-pigments do not pre-exist as such in the blood. 



71. With regard to the source of the various components of the Biliary ex- 

 cretion which have been now described, our information is much less precise 

 than it is with respect to the principal excretory matters of the Urine. This 

 arises, not merely from the difficulties already adverted to as attending the 

 chemical determination of the true constituents of Bile ; but also from the fact 

 that the detection of their presence in the blood by no means implies their pre- 

 existence in the circulating fluid. For, as we shall hereafter see (CHAP. Vii.), 

 there is strong reason to believe that a considerable proportion of the solid mat- 

 ters of the bile, which are poured into the upper part of the intestinal tube, are 

 normally reabsorbed, and again introduced into the current of the circulation, 

 before reaching the outlet ; and it is quite certain that such reabsorption may 

 take place in cases of obstruction in the biliary ducts, when the bile is secreted, 

 but cannot find its way into the alimentary canal. Hence, neither the detection 

 of cholic acid in the blood by Pettenkofer's test which has been occasionally 

 accomplished, even in cases of disease in which the liver did not seem impli- 



