308 ASSIMILATING ACTION OF LIVER. 
would appear as if the nutritive materials, in their ultimate 
metamorphosis, resolved themselves chiefly into these two 
excretory products. The greater part of the biliary matter 
poured into the intestinal canal seems to be ordinarily re¬ 
absorbed with the fatty matter of the food, and to be, like it, 
carried out of the system through the lungs in the form of 
carbonic acid and water; it being only when the bile has 
either been formed in excessive amount, or has been pro¬ 
pelled along the intestinal tube with undue activity, that it is 
discharged in any quantity from the rectum, as in bilious 
diarrhoea.—The secreting action of the Liver, however, is by 
no means its sole mode of influencing the composition of the 
blood; for it has been shown by the recent researches of 
M. Bernard, that the blood which leaves the liver by the 
hepatic vein contains a peculiar substance of a saccharine 
nature, 1 which does not exist in the blood brought to the 
organ by the portal vein. This substance appears to be 
elaborated by the converting power of the liver, either from 
materials supplied by the food, or from the products of the 
waste of the system ; and it seems to be specially destined as 
a pabulum or fuel for the combustive process, being usually 
eliminated from the blood in the form of carbonic acid and 
water during its passage through the lungs, so as not to pass 
into the systemic circulation unless either its quantity be un¬ 
usually great, or its elimination be interfered with by imperfect 
respiration. The liver seems also to form a peculiar fat, which 
is usually consumed in the same manner; but if the respiratory 
process be feeble, this fat accumulates in the cells of the liver 
itself. 
367. The TJrinary excretion has for its chief purpose to 
throw off those products, formed in a similar manner, which 
are highly charged with azote. The most important of its 
ingredients, in Man and the Mammalia, is the substance termed 
Urea , which has a crystalline form, and is very soluble in 
water. It contains 2 equivalents of Carbon, 4 of Hydrogen, 
2 of Azote, and 2 of Oxygen; and it will be seen, by referring 
to the statement formerly given of the composition of albumen 
1 This substance is spoken of by M. Bernard as sugar : it has been 
demonstrated, however, by the recent researches of Dr. Pavy, that the 
liver does not form sugar, but a substance that becomes sugar almost 
immediately upon contact with albuminous matters. 
