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ON THE NATURAL FACULTIES Book I
[p. 89]much more rarefied there than it is amongst the corn, yet it does not take up a tenth part of the moisture which the corn does.
Since, then, we have talked sufficient nonsense- not willingly, but because we were forced, as the proverb says, "to behave madly among madmen"- let us return again to the subject of urinary secretion. Here let us forget the absurdities of Asclepiades, and, in company with those who are persuaded that the urine does pass through the kidneys, let us consider what is the character of this
function. For, most assuredly, either the urine is conveyed by its own motion to the kidneys, considering this the better course (as do we when we go off to market!
Playful suggestion of free-will in the urine.
), or, if this be impossible, then some other reason for its conveyance must be found. What, then, is this? If we are not going to grant the kidneys a faculty for attracting this particular quality,
Specific attraction. cf. p. 87, note 2.
as Hippocrates held, we shall discover no other reason. For, surely everyone sees that either the kidneys must attract the urine, or the veins must propel it- if, that is, it does not move of itself. But if the veins did exert a propulsive action when they contract, they would squeeze out into the kidneys not merely the urine, but along with it the whole of the blood which they contain.
i.e. there would be no selective action.
And if this is impossible, as we shall show, the remaining explanation is that the kidneys do