The Urinary System

Asclepiades absurdly believes that the urine does pass through the kidneys.

If we are not going to grant the kidneys a faculty for attracting this particular quality,135 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.136 And if this is impossible, as we shall show, the remaining explanation is that the kidneys do exert traction.

How is propulsion by the veins impossible?

The situation of the kidneys is against it. They do not occupy a position beneath the hollow vein [vena cava] as does the sieve-like [ethmoid] passage in the nose and palate in relation to the surplus matter from the brain;137 they are situated on both sides of it. Besides, if the kidneys are like sieves, and readily let the thinner serous [whey-like] portion through, and keep out the thicker portion, then the whole of the blood contained in the vena cava must go to them, just as the whole of the wine is thrown into the filters.

Further, the example of milk being made into cheese will show clearly what I mean. For this, too, although it is all thrown into the wicker strainers, does not all percolate through; such part of it as is too fine in proportion to the width of the meshes passes downwards, and this is called whey [serum]; the remaining thick portion which is destined to become cheese cannot get down, since the pores of the strainers will not admit it. Thus it is that, if the blood-serum has similarly to percolate through the kidneys, the whole of the blood must come to them, and not merely one part of it.

What, then, is the appearance as found on dissection?

One division of the vena cava is carried upwards138 to the heart, and the other mounts upon the spine and extends along its whole length as far as the legs; thus one division does not even come near the kidneys, while the other approaches them but is certainly not inserted into them. Now, if the blood were destined to be purified by them as if they were sieves, the whole of it would have to fall into them, the thin part being thereafter conveyed downwards, and the thick part retained above.

But, as a matter of fact, this is not so. For the kidneys lie on either side of the vena cava. They therefore do not act like sieves, filtering fluid sent to them by the vena cava, and themselves contributing no force. They obviously exert traction; for this is the only remaining alternative.

How, then, do they exert this traction? If, as Epicurus thinks, all attraction takes place by virtue of the rebounds and entanglements of atoms, it would be certainly better to maintain that the kidneys have no attractive action at all; for his theory, when examined, would be found as it stands to be much more ridiculous even than the theory of the lodestone, mentioned a little while ago. Attraction occurs in the way that Hippocrates laid down; this will be stated more clearly as the discussion proceeds; for the present our task is not to demonstrate this, but to point out that no other cause of the secretion of urine can be given except that of attraction by the kidneys,139 and that this attraction does not take place in the way imagined by people who do not allow Nature a faculty of her own.140

For if it be granted that there is any attractive faculty at all in those things which are governed by Nature,141 a person who attempted to say anything else about the absorption of nutriment142 would be considered a fool.

XVI

Erasistratus[143] replied at great length to certain other foolish doctrines.

He entirely passed over the view held by Hippocrates, not even thinking it worth while to mention it, as he did in his work “On Deglutition”; in that work, as may be seen, he did go so far as at least to make mention of the word attraction, writing somewhat as follows:

“Now, the stomach does not appear to exercise any attraction.”143 But when he is dealing with anadosis he does not mention the Hippocratic view even to the extent of a single syllable. Yet we should have been satisfied if he had even merely written this: “Hippocrates lies in saying ‘The flesh144 attracts both from the stomach and from without,’ for it cannot attract either from the stomach or from without.”

Or if he had thought it worth while to state that Hippocrates was wrong in criticizing the weakness of the neck of the uterus, “seeing that the orifice of the uterus has no power of attracting semen,”145 or if he [Erasistratus] had thought proper to write any other similar opinion, then we in our turn would have defended ourselves in the following terms:

“My good sir, do not run us down in this rhetorical fashion without some proof; state some definite objection to our view, in order that either you may convince us by a brilliant refutation of the ancient doctrine, or that, on the other hand, we may convert you from your ignorance.” Yet why do I say “rhetorical”?

For we too are not to suppose that when certain rhetoricians pour ridicule upon that which they are quite incapable of refuting, without any attempt at argument, their words are really thereby constituted rhetoric.

For rhetoric proceeds by persuasive reasoning; words without reasoning are buffoonery rather than rhetoric. Therefore, the reply of Erasistratus in his treatise “On Deglutition” was neither rhetoric nor logic. For what is it that he says?

“Now, the stomach does not appear to exercise any traction.” Let us testify against him in return, and set our argument beside his in the same form. Now, there appears to be no peristalsis146 of the gullet.

“And how does this appear?” one of his adherents may perchance ask. “For is it not indicative of peristalsis that always when the upper parts of the gullet contract the lower parts dilate?” Again, then, we say, “And in what way does the attraction of the stomach not appear? For is it not indicative of attraction that always when the lower parts of the gullet dilate the upper parts contract?”

Now, if he would but be sensible and recognize that this phenomenon is not more indicative of the one than of the other view, but that it applies equally to both,147 we should then show him without further delay the proper way to the discovery of truth.

We will, however, speak about the stomach again. And the dispersal of nutriment [anadosis] need not make us have recourse to the theory regarding the natural tendency of a vacuum to become refilled,148 when once we have granted the attractive faculty of the kidneys. Now, although Erasistratus knew that this faculty most certainly existed, he neither mentioned it nor denied it, nor did he make any statement as to his views on the secretion of urine.

Why did he give notice at the very beginning of his “General Principles” that he was going to speak about natural activities—firstly what they are, how they take place, and in what situations—and then, in the case of urinary secretion, declared that this took place through the kidneys, but left out its method of occurrence?

It must, then, have been for no purpose that he told us how digestion occurs, or spends time upon the secretion of biliary superfluities;149 for in these cases also it would have been sufficient to have named the parts through which the function takes place, and to have omitted the method.

On the contrary, in these cases he was able to tell us not merely through what organs, but also in what way it occurs—as he also did, I think, in the case of anadosis; for he was not satisfied with saying that this took place through the veins, but he also considered fully the method, which he held to be from the tendency of a vacuum to become refilled. Concerning the secretion of urine, however, he writes that this occurs through the kidneys, but does not add in what way it occurs. I do not think he could say that this was from the tendency of matter to fill a vacuum,150 for, if this were so, nobody would have ever died of retention of urine, since no more can flow into a vacuum than has run out.

For, if no other factor comes into operation151 save only this tendency by which a vacuum becomes refilled, no more could ever flow in than had been evacuated. Nor could he suggest any other plausible cause, such, for example, as the expression of nutriment by the stomach152 which occurs in the process of anadosis; this had been entirely disproved in the case of blood in the vena cava;153 it is excluded, not merely owing to the long distance, but also from the fact that the overlying heart, at each diastole, robs the vena cava by violence of a considerable quantity of blood.

In relation to the lower part of the vena cava154 there would still remain, solitary and abandoned, the specious theory concerning the filling of a vacuum. This, however, is deprived of plausibility by the fact that people die of retention of urine, and also, no less, by the situation of the kidneys. For, if the whole of the blood were carried to the kidneys, one might properly maintain that it all undergoes purification there. But, as a matter of fact, the whole of it does not go to them, but only so much as can be contained in the veins going to the kidneys;155 this portion only, therefore, will be purified.

Further, the thin serous part of this will pass through the kidneys as if through a sieve, while the thick sanguineous portion remaining in the veins will obstruct the blood flowing in from behind; this will first, therefore, have to run back to the vena cava, and so to empty the veins going to the kidneys; these veins will no longer be able to conduct a second quantity of unpurified blood to the kidneys—occupied as they are by the blood which had preceded, there is no passage left. What power have we, then, which will draw back the purified blood from the kidneys?

And what power, in the next place, will bid this blood retire to the lower part of the vena cava, and will enjoin on another quantity coming from above not to proceed downwards before turning off into the kidneys?

Erasistratus realized that all these ideas were open to many objections.

He could only find one idea which held good in all respects—namely, that of attraction.

Since, therefore, he did not wish either to get into difficulties or to mention the view of Hippocrates, he deemed it better to say nothing at all as to the manner in which secretion occurs.

But even if he kept silence, I am not going to do so. For I know that if one passes over the Hippocratic view and makes some other pronouncement about the function of the kidneys, one cannot fail to make oneself utterly ridiculous.

It was for this reason that Erasistratus kept silence and Asclepiades lied; they are like slaves who have had plenty to say in the early part of their career, and have managed by excessive rascality to escape many and frequent accusations, but who, later, when caught in the act of thieving, cannot find any excuse; the more modest one then keeps silence, as though thunderstruck, whilst the more shameless continues to hide the missing article beneath his arm and denies on oath that he has ever seen it.

For it was in this way also that Asclepiades, when all subtle excuses had failed him and there was no longer any room for nonsense about “conveyance towards the rarefied part [of the air],”156 and when it was impossible without incurring the greatest derision to say that this superfluity [i.e. the urine] is generated by the kidneys as is bile by the canals in the liver—he, then, I say, clearly lied when he swore that the urine does not reach the kidneys, and maintained that it passes, in the form of vapour, straight from the region of the vena cava,157 to collect in the bladder.

Like slaves, then, caught in the act of stealing, these two are quite bewildered, and while the one says nothing, the other indulges in shameless lying.