THE PRINCIPLE OF VITAL AFFINITY. 335 



matters are converted before they are excreted, contain a much larger proportion 

 of oxygen than those compounds themselves ; and, thirdly, that it is also neces- 

 sarily applied to all dead animal matter when the decomposition, leading to the 

 same ultimate results, takes place in it. 



It is true that the Bile does not contain a larger proportion of oxygen than 

 albumen, but it contains a larger proportion than any kind of oil or fat, from 

 which it appears certain that it is partly formed ; and, farther, we have perfectly 

 good evidence, very well stated by Liebig, that by far the greater part of the 

 bile in all animals, and nearly the whole in the carnivora, is re-absorbed into the 

 blood, and exposed gradually to the action of oxygen on it above indicated, and 

 therefore that the secretion of the liver, so far as it is destined to excretion, re- 

 solves itself chiefly into the excretion of carbonic acid and Avater by the skin and 

 lungs, and partially also into that of urea and uric acid by the kidneys ; which 

 arrangement, we have reason to believe, is designed with a view to the main- 

 tenance of animal heat, to be considered afterwards. 



It may here be a question, whether the simply chemical attraction of the 

 oxygen, carried to the extremities of the vessels in the blood, is the cause, or part 

 of the cause, of the act of absorption, antagonizing the strictly vital attraction by 

 which the elements of nutrition are brought into the cells of the textures. But 

 the power exercised by the excretory glands themselves appears manifestly to be 

 merely that of selection and attraction of the material destined to pass out by 

 them, by an agency of cells quite analogous to that by which the cells of the 

 textures appropriate their own nourishment ; and by this simple and beautiful 

 principle, of certain cells, or the cells in a certain part of the structui'e, exerting a 

 peculiar attraction for certain matters only, existing in the compound fluid pre- 

 sented to them, nature has provided both for the nutrition and growth of all the 

 textures, and for the expulsion of such matters as must be evolved from the 

 blood, and have not such a property of volatility as might enable them to pass off" 

 by the skin and lungs. 



It may be objected to the statement now made as to the respective provinces 

 of vital and simply chemical affinities, that vegetable and animal substances re- 

 moved from the living structures which formed them, are often of long and 

 nearly indefinite duration ; but it would be an error to infer from this fact, that 

 the affinities which led to their formation act as long as they endure ; we can 

 only infer that the conditions, under which other chemical affinities act on such 

 compounds, are not present ; and the general property of the inertia of matter 

 prevents their changing the condition into which they have been once brought, 

 just as the same substance reduced to the state of charcoal may remain long 

 xmaltered, although in contact with oxygen, and liable to an affinity with that 

 gas, which, under a slight variation of circumstances, would convert it into car- 



