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ment to the whole body. For unless we are agreed upon the first point, any ulterior, any more operose, discussion of their nature, is in vain. But how can these vessels serve as con- duits for the whole of the chyle, or the nourishment of the body, when we see that they are different in different animals? In some they proceed to the liver, in others to the porta only, and in others still to neither of these. In some creatures they are seen to be extremely numerous in the pancreas ; in others the thymus is crowded with them ; in a third class, again, nothing can be seen of them in either of these organs. In some animals, indeed, such chyliferous canals are nowhere to be discovered (vide Liceti Epist. xiii, tit. ii, p. 83, et Sen- nerti Praxeos, lib. v, tit. 2, par. 3, cap.]); neither do they exist in any at all times. But the vessels which serve for nutri- tion must necessarily both exist in all animals, and present themselves at all times ; inasmuch as the waste incurred by the ceaseless efflux of the spirits, and the wear and tear of the parts of the body, can only be supplied by as ceaseless a restoration or nutrition. And then, their very slender calibre seems to render them not less inadequate to this duty than their structure seems to unfit them for its performance : the smaller channels ought plainly to end in larger ones, these in their turn in channels larger still, and the whole to concentrate in one great trunk, which should correspond in its dimensions to the aggregate capacity of all the branches; just such an arrangement as may be seen to exist in the vena portse and its tributaries, and farther in the trunk of the tree, which is equal to its roots. Wherefore, if the efferent canals of a fluid must be equal in dimensions to the afferent canals of the same fluid, the chyliferous ducts which Pecquet discovers in the thorax, ought at least to equal the two ureters in dimensions; otherwise they who drink a gallon or more of one of the acidulous waters could not pass off all this fluid in so short a space of time by these vessels into the bladder. And truly, when we see the matter of the urine passing thus copiously through the appro- priate channels, I do not see how these veins could preserve their milky colour, and the urine all the while remain without a tinge of whiteness.
I add, too, that the chyle is neither in all animals, nor at all times, of the consistency and colour of milk ; and therefore
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