SECRETION OF BILE. 307 
sugary substance that is derivable from the decomposition of 
gelatin and albumen) and with taurine (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- 
cholic, which are mingled in different proportions im 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 te 
the other. Thus we find in Insects, a respiratory system 
ing 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 ap 
__ 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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