The Nature of Urine

Those near the times of Erasistratus maintain that the parts above the kidneys receive pure blood, whilst the watery residue, being heavy, tends to run downwards.

This then percolates through the kidneys themselves, is thus rendered serviceable, and is sent, as blood, to all the parts below the kidneys.

For a certain period this view found favour and flourished and was held to be true.

After a time, however, it became suspect to the Erasistrateans themselves, and finally they abandoned it because of 2 points:

1. The heaviness of the serous fluid

This was said to be produced in the vena cava. It did not exist, apparently, at the beginning, when this fluid was being carried up from the stomach to the liver.

Why, then, did it not at once run downwards when it was in these situations? And if the watery fluid is so heavy, what plausibility can anyone find in the statement that it assists in the process of anadosis?

2. The assertion that all the watery fluid falls downwards only when it is in the vena cava

How is it going to fall into the kidneys, seeing that these are not situated below, but on either side of the vena cava, and that the vena cava is not inserted into them, but merely sends a branch into each of them, as it also does into all the other parts?

This doctrine was replaced by a more foolish one saying that if oil be mixed with water and poured upon the ground, each will take a different route:

• the one flowing this way
• the other that way

And so the watery fluid runs into the kidneys, while the blood falls downwards along the vena cava.

This doctrine was already condemned.

For why, of the countless veins which spring from the vena cava, should blood flow into all the others, and the serous fluid be diverted to those going to the kidneys? They have not answered the question which was asked; they merely state what happens and imagine they have thereby assigned the reason.

The worst doctrine of all was lately invented by Lycus of Macedonia161. It is popular due to its novelty.

He asserts that urine is residual matter from the nutrition of the kidneys!162

The amount of urine passed every day shows clearly that it is the whole of the fluid drunk.

These people rapidly pass almost the same quantity as they drink.

Even Erasistratus was aware of this is his “General Principles” Book 1.

Thus Lycus is speaking only from himself.

Now it is agreed that all parts which are undergoing nutrition produce a certain amount of residue, but it is neither agreed nor is it likely, that the kidneys alone, small bodies as they are, could hold four whole congii,164 and sometimes even more, of residual matter.

For this surplus must necessarily be greater in quantity in each of the larger viscera; thus, for example, that of the lung, if it corresponds in amount to the size of the viscus, will obviously be many times more than that in the kidneys, and thus the whole of the thorax will become filled, and the animal will be at once suffocated.

But if it be said that the residual matter is equal in amount in each of the other parts, where are the bladders, one may ask, through which it is excreted?

For, if the kidneys produce in drinkers three and sometimes four congii of superfluous matter, that of each of the other viscera will be much more, and thus an enormous barrel will be needed to contain the waste products of them all.

Yet one often urinates practically the same quantity as one has drunk, which would show that the whole of what one drinks goes to the kidneys.

Thus the author of this third piece of trickery would appear to have achieved nothing, but to have been at once detected, and there still remains the original difficulty which was insoluble by Erasistratus and by all others except Hippocrates.

I dwell purposely on this topic, knowing well that nobody else has anything to say about the function of the kidneys, but that either we must prove more foolish than the very butchers if we do not agree that the urine passes through the kidneys; or, if one acknowledges this, that then one cannot possibly give any other reason for the secretion than the principle of attraction.

Now, if the movement of urine does not depend on the tendency of a vacuum to become refilled,166 it is clear that neither does that of the blood nor that of the bile; or if that of these latter does so, then so also does that of the former. For they must all be accomplished in one and the same way, even according to Erasistratus himself.

This matter will be discussed in Book 2.