406 OF SECRETION. 



that it cannot be (as supposed by Liebig) the chief fuel of the process 

 of combustion, which is kept up through the agency of those organs. 

 The secreting action of the Liver, by which a certain product is entirely 

 separated from the blood, constitutes, however, only a part of the action 

 of that organ ; since, as already shown ( 493), the changes which it 

 effects in the alimentary materials newly introduced into the current 

 of the circulation, are at least equally important. A large part of the 

 bulk of the Liver, in many of the lower- animals, is made up of oleagi- 

 nous matter; which appears to accumulate in the hepatic cells, giving 

 them almost the character of fat-cells, in proportion as the respiratory 

 function is inactive. Thus, the liver is very large and fatty in Mollusca 

 and Crustacea; whilst, on the other hand, in Insects it is comparatively 

 undeveloped. In Fishes, again, it is rich in oily matter, but in Mam- 

 malia it is much less fatty in the state of health ; whilst in the liver of 

 Birds, scarcely any traces of fat are to be found. 

 1 726. The elements of the bile may be altogether supplied by the 

 disintegration of the tissues ; and this must certainly be the case, when 

 the amount of food taken is no more than enough to supply the waste 

 of the system. We may regard it, then, as one office of the Liver, to 

 remove from the blood such products of that disintegration, as are rich 

 in carbon and hydrogen. It may be pretty certainly affirmed, however, 

 that biliary matter does not pre-exist as such in the blood ; but that its 

 elements must be originally present there, under some more pernicious 

 form. For it is found that the total suspension of the secreting action 

 of the Liver, whereby the excrementitious matter is left to accumulate 

 in the blood, has a much more prejudicial effect upon the system, than 

 the reabsorption of Bile after it has been secreted, in consequence of 

 an obstruction to its discharge through the ductus choledochus ; so that 

 it may be inferred that the noxious products of the disintegration of 

 the tissues are transformed into the comparatively innocent components 

 of Bile, in the very act of secretion. But there can be little doubt, 

 that the Liver has also for its office, to draw off from the blood any 

 superfluity which may exist in the non-azotized compounds derived from 

 the food, beyond the amount that is requisite for the supply of the 

 respiratory process, or that can be deposited as fat. For we conti- 

 nually witness the results of habitual excess in the amount of such sub- 

 stances, in producing that state of the system commonly termed bilious ; 

 of which all the symptoms are referable to the accumulation of the ele- 

 ments of the bile in the blood, and the consequent deterioration in the 

 purity of the circulating fluid. Where a tendency to such a state 

 exists, proper means should be taken to stimulate the liver to increased 

 activity ; but the chief reliance should be placed on the avoidance of 

 those articles of diet, which contain a large proportion of non-azotized 

 matter, and on abstinence from superfluous nutriment of any de- 

 scription. 



3. Of the Kidneys and the Urine. 



727. The Kidneys are perhaps the most purely excreting organs in 

 the body ; their function being to separate from the blood certain matters 



