LETTERS. 607
did these vessels carry chyle, they could not always (which nevertheless they do) contain a white fluid in their interior, but would sometimes be coloured yellow, green, or of some other hue (in the same way ' as the urine is affected, and acquires different colours from eating rhubarb, asparagus, figs, &c.) ; or otherwise, when large quantities of mineral water were drunk, they would be deprived of almost all colour. Besides, did that white matter pass from the intestines into those canals, or were it attracted from the intestines, the same fluid ought certainly to be discovered somewhere within the intes- tines themselves, or in their spongy tunics ; for it does not seem probable that any fluid by bare and rapid percolation of the intestines could assume a new nature, and be changed into milk. Moreover, were the chyle only filtere"d through the tunics of the intestines, it ought surely to retain some traces of its original nature, and resemble in colour and smell the fluid contained in the intestines ; it ought to smell offen- sively at least ; for whatever is contained in the intestines is tinged with bile, and smells unpleasantly. Some have conse- quently thought that the body was nourished by means of chyle raised into attenuated vapour, because vapours exhaling in the alembic, even from fetid matters, often do not smell amiss.
The learned Pecquet ascribes the motion of this milky fluid to respiration. For my own part, though strongly tempted to do otherwise, I shall say nothing upon this topic until we are agreed as to what the fluid is. But were we to concede the point (which Pecquet takes for granted without any suf- ficient reason in the shape of argument), that chyle was con- tinually transported by the canals in question from the intes- tines to the subclavian veins, in which the vessels he has lately discovered terminate, we should have to say that the chyle be- fore reaching the heart was mixed with the blood which is about to enter the right side of the organ, and that it there obtains a further concoction. But what, some one might with as good reason ask, should hinder it from passing into the porta, then into the liver, and thence into the cava, in conformity with the arrangement which Aselli and others are said to have found ? Why, indeed, should we not as well believe that the chyle enters the mouths of the mesenteric veins, and in this
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