SECRETION OF BILE. 307 



sugary substance that is derivable from the decomposition of 

 gelatin and albumen) and withtaurine (a substance distinguished 

 for the large proportion of sulphur it contains, no less than 

 25 per cent), two other acids, the Glycocholic and the Tauro- 

 cholicj which are mingled in different proportions in the bile 

 of different animals, both being combined with soda as a base. 

 Bile also contains a white crystallizable fatty substance 

 resembling spermaceti, which is termed Cholesterin ; this 

 consists of 36 Carbon, 32 Hydrogen, and 1 Oxygen; and 

 though its quantity in healthy bile appears to be very small, 

 yet it occasionally increases to such an extent as to form the 

 concretions known as "gall-stones," which, getting into the 

 bile-duct, are transmitted along it with great pain and diffi- 

 culty, or block it up altogether. The peculiar colouring 

 matter of bile is quite distinct from the preceding substances ; 

 but like them it is extremely rich in carbon and hydrogen. 



365. The bulk of the Liver, and the activity of the Respira- 

 tory apparatus, seem generally to bear an inverse ratio one to 

 the other. Thus we find in Insects, a respiratory system 

 possessing enormous extension and activity of function, and a 

 liver so slightly developed, that for a long time it was not 

 recognised as such. On the other hand, in the Mollusca, we 

 find the respiration carried-on upon a lower plan, and with 

 far less activity; but the liver is of enormous size, often 

 making up a large part of the bulk of the body. Moreover, 

 in the Crustacea, which are formed upon the same general 

 plan with Insects, but which have an aquatic and therefore 

 less energetic respiration, we find the liver very large, as in 

 the Mollusca. In Reptiles and Fishes, again, whose respira- 

 tion and temperature are low, the liver is comparatively larger 

 than in Birds and Mammals, in which classes the respiration 

 is more energetic, and the blood warm. In all these in- 

 stances, however, the bulk of the liver depends in great part 

 upon the accumulation of fat in its cells ; and the secreting 

 activity may be positively less in them, than it is in animals 

 which have a comparatively small biliary apparatus. 



366. The materials of the secretion of Bile are probably 

 derived in part from the disintegration of the tissues, and in 

 part more directly from the food. It is an interesting fact 

 that the composition of bile and urine, taken together, corre- 

 sponds closely with the composition of the blood ; so that it 



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