than the catheter, and bent down like the body of a retort, so that the fragments can fall to the bottom of it; and the instrument will still work well if it has joints made, for economy, of cork or rubber instead of metal. But, however otherwise arranged, a satisfactory aspirator should have —

4. Some device, near the catheter, to act as a trap for débris and secure every fragment that has passed it.

The chief difference among evacuators now is in the degree of certainty with which they retain the fragments they have aspirated. Any instrument will draw out the fragments, but few hold them securely; for the débris do not always fall into the glass receiver, nor do they always remain in it. On the contrary, they are easily carried back to the bladder. This defect in the action of the evacuator has received little attention from surgeons, although it is the only point connected with the evacuator which offers any difficulty whatever. Until recently it has been remedied only by sacrificing simplicity in the apparatus.

In endeavoring to make a satisfactory evacuator for litholapaxy, many experiments have to be tried. It is quite possible that a perfectly satisfactory instrument might have been contrived some time ago if it had been generally understood that an evacuator that works best with pieces of broken coal in a vessel of water will succeed best with the fragments in the bladder. So also will the surgeon if he is otherwise well qualified. It is true that the living tissues are easily injured, but in other respects the experiment can be made sufficiently like the operation to give it great value. Aspirating débris from the bladder is not a question of pathology, but of operative surgery, of physics; and in view of the fact that we fail, in some bladders, to discover a last fragment even by repeated washing, an evacuator should be so constructed that

1 The specific gravity of hard coal is 1.575. That of a urate calculus is 1.540, and of a mulberry calculus, 1.262.

it will absolutely prevent a fragment that has once passed the catheter from returning to the bladder to become the nucleus of another calculus.

As

It is not altogether easy to meet this requirement, because the solid particles are usually borne back and forth with the current of water. In a common evacuator, they are carried wherever the current goes, - first from the bladder to the bulb, and then, when it is reversed, back to the bladder, a part only falling into the receiver at each aspiration. we may fairly assume that a surgeon would not deliberately inject foreign bodies into a patient's bladder, there must be something wrong in a system which obliges him to do this, and makes it necessary to aspirate the same débris twenty times over in order to remove it. In short, the apparatus as commonly arranged is still a defective one, and needs some special contrivance to assist the action of gravity in securing the débris.

Surgeons have long felt this. The use of an elastic tube connected with the catheter has been more than once criticised, and with some reason, on the ground that it might contain fragments which would be returned to the bladder; and again, in order to shorten by an inch the route from the bladder, a less convenient stop-cock has been substituted for the usual one. But lithotritists should be fully aware of the fact that whether there is an elastic tube or not, a tenfold greater quantity of fragments is generally driven back out of the bulb itself, and that the difficulty lies almost wholly in that part of the instrument. At each expansion débris are drawn from the bladder into the bulb, where they are delayed until, when it is compressed, they are injected back into the bladder. Only a part of them, sometimes only the larger half (the quantity varying in different instruments), settle into the glass receiver. This important fact, so little recognized, should not be accepted without demonstration.

An instrument which Sir Henry Thompson has lately abandoned (Fig. 1) can be made to demonstrate exactly how the currents act upon the fragments, in an evacuator which is unprovided with a catheter-trap to prevent them from reentering the bladder. It is here selected because the peculiar form of this instrument makes it easy to fit a glass tube to it so that we can see what takes place in the interior. Let a piece of glass tube an inch in diameter be inserted at the joint JJ, between the bulb B and the catheter, to show what passes with the current from one to the other in either direction. If the end of the catheter be now placed in a suitable vessel of water containing fragments of coal of different sizes, while the bulb is alternately compressed and allowed to dilate, a continued stream of fragments will be seen rising from the vessel into the bulb, and then returning to the vessel, as they inevitably would do to the bladder. The back-flow of débris can be still better watched if a glass tube be also substituted for the catheter, as in the figure.

But there is another important fact illustrated by this instrument. Fragments do not always stay in a receiver after they have been deposited there. When the glass receiver R of this evacuator is half filled with fragments, a part of these are easily carried back into the vessel or into the bladder. They are first lifted up from the receiver into the bulb, and then driven out through the catheter; for though the orifice of this glass receiver is small and protected by a special trap, the current and débris pass out of it as well as into it. It could not have been foreseen that fragments would escape from a receptacle apparently so well arranged; but it will be found that in any instrument, if the bulb or catheter directs the current into the glass receiver, whether directly or obliquely, fragments are easily carried out again.

The general result is little better, if, to avoid stirring the fragments which lie in the receiver, the current is directed

horizontally over the mouth of it instead of into it. Some of them then pass directly back and forth between the bladder and the bulb, over the receiver, without falling into it. This defect can be shown in an instrument recently employed by Sir Henry at the suggestion of Weiss and Co.,1 where the stream from the catheter passes horizontally through an empty chamber on its way to the bulb. As the stream enters it, its velocity is so diminished that fragments fall to the bottom into the receiver, and in greater number when the bulb is weak. Many fragments are of course secured. But, to be wholly effectual, the chamber intended to retard and break up the current by its size would have to be inconveniently large, in order to give time to the floating débris entering on one side to settle into the receiver without passing farther. The principle here involved is quite different from that of the evacuator represented in the above figure. This instrument is not unlike one formerly figured in the "Lancet; "2 but the valve and strainer which there act as a trap have been omitted, and, in consequence, not a few fragments escape back to the bladder.

In Weiss's evacuator again, some of the fragments which enter the bulb gather in the bottom of it, which is lower than its outlet, and where there is no receiver to collect them. The chief difficulty, however, is not that these fragments stray into the bulb, but that for want of a trap they are afterward liable to escape out of it and back to the bladder.

This difficulty is not wholly obviated by placing a strainer across the mouth of the bulb to prevent the fragments from entering it, as has been done in some other evacuators. Let me mention in this connection the results of a former experiment. It might be supposed that if the passing fragments were arrested by a flat strainer placed across the current, whether at the orifice of the bulb or elsewhere, they would

1 Lancet, January 7, 1882.

2 Lancet, September 24, 1881, Fig. 5. (See pp. 300, 301, of this volume.)