DIGESTION. 177 



ular cell with their network. These interior communicating passages 

 are the capillary bile-ducts. They are much smaller than the capillary 

 blood-vessel.-, being in the rabbit's liver, according to Kb'lliker, not 

 more than 2 mmm. in diameter. They embrace the glandular cells in 

 such a way that they are always situated at the greatest possible dis- 

 tance, that is, half the diameter of a cell, from the nearest capillary 

 blood-vessel ; the blood-vessels running along the edges of the pris- 

 matic cells (Kb'lliker), while the ducts pass along the middle of their 

 plane surfaces. Thus the two sets of canals, namely, capillary blood- 

 vessels and bile-ducts, form a double series of inosculating passages 

 embracing the glandular cells, and directed at right angles to each other. 



Physical Properties and Composition of the Bile. 



The bile, as it comes from the gall-bladder, is a clear, more or less 

 ropy fluid, of neutral or alkaline reaction, with a faint animal odor. Its 

 average specific gravity, according to various observers, .is about 1020. 

 If shaken with air, it foams up into a frothy mixture, which remains 

 for a long time on its surface. This property depends on the presence 

 of the biliary salts, which have the same action in a watery solution. ; 

 The ropy character of the secretion varies much at different times, even 

 in the same animals, and is due to the mucus of the gall-bladder ; as 

 the bile which flows directly from the hepatic ducts is always a watery 

 fluid. The longer it is retained in the gall-bladder, the more dense and 

 mucous is its consistency. 



The color of the bile varies, in different species of animals, from a 

 reddish-orange to a nearly pure green, presenting all the intermediate 

 tints of golden-yellow, reddish-brown, olive-brown, olive, yellowish- 

 green, and bronze-green. Human bile from a biliary fistula was found 

 by Jacobsen to be clear, yellowish, bronze-green ; that taken from the 

 gall-bladder after death is usually a dark golden-brown. Dog's bile is 

 brownish-olive or bronze ; pig's bile reddish-orange or reddish-brown ; 

 and sheep- and ox-bile greenish-olive, or more frequently nearly green. 

 As a rule, the bile of herbivorous animals is more decidedly green, that 

 of the carnivora and omnivora orange or brown. These differences 

 may be referred to two principal tints, corresponding with the two 

 coloring matters of bile ; in one of which the predominating color is 

 red or reddish-brown, dependent on bilirubine, in the other green, 

 owing to the presence of bilirerdine. As their proportion varies, the 

 specimen will exhibit a corresponding color of the pure or mingled tints. 



The color of the bile is also modified by oxidizing agents, which 

 produce a green hue in olive or brown bile, and increase the intensity 

 of the green when this color is already present. If brown- or olive- 

 colored bile be exposed for a short time, its surface becomes green by 

 contact with the atmosphere. The change may be instantly produced 

 by adding a few drops of a watery solution of iodine ; and a little nitric 

 acid acts with great energy, developing at once a bright grass-green 

 hue. The color of green bile, on the other hand, disappears by exclu- 



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