to that from within, outwards; for it is certain that their splitting was the effect of the pressure of some small stones acting as wedges against their extremities. No dissolvent by any conceivable action upon a tube, could have divided it into two nearly equal parts.

I then got a parcel of tin tubes made, whose small diameter rendered them capable of sustaining much longer efforts, the diameters of their hollow being, at most, but a line and three quarters; and, to add to their strength, they were covered a line and a half thick with solder, which also closed up their orifices; they were about seven lines long. I caused a turkey to swallow one of them; to another I gave two; and to a third six at once. When I opened these birds 24 hours, and two days after, I could not find a single tube whose solidity had been proof against the force that attacked it. That which had suffered the least was grooved from end to end on two opposite sides; most of the rest were absolutely flattened, and some of them in part unrolled; the little plates that had been firmly soldered to their ends, were forced away, some of them being driven into the tubes, and others pushed outwards.

What a mighty resistance must the gizzard have been able to overcome in flattening these tubes, and producing the other remarkable alterations in their figure! The result of the different trials I made upon the like tubes, may serve in some measure to convey an idea of it: several of these, for instance, I squeezed between the cheeks of a vice, by hanging weights on the end of the handle; and it required about 437 pounds to flatten them as the gizzard had done.

A large nut with its shell is easily ground to pieces in a turkey's gizzard; and the recipe for fattening them by giving them one or two a day, is not so ridiculous as may at first appear. I have carried the point so far as to force four and twenty large ones into a turkey's craw at once, where they might be heard to rattle, upon filliping the neck on the outside; next morning they were all gone, having undergone the operation of grinding, in the gizzard.

But notwithstanding this amazing force which the gizzard exerts, in grinding the aliment it receives, does it not require the assistance of a dissolvent? And is not such a one actually to be found there?-The force of the gizzard, great as it is, has its limits; and I have cast lead in moulds, whose shape it could not alter. Into one leaden tube, left open at each end, I introduced a grain of raw barley, with its husk on; into another a grain of the same husked, and into a third a grain boiled till it was ready to crack. These

tubes continued at least twenty-four hours, and sometimes double that space, in a turkey's gizzard; and the experiment was repeated divers times.-The grain, whether raw and in its husk, or without the husk, or boiled, perfectly retained its figure and solidity, without any sensible alteration, except perhaps a little swelling, such as it would have acquired in any moist place.

It is well known how quickly ducks digest flesh food. I caused one to swallow several leaden tubes, in each of which was a bit of raw beef or veal, of the size of a barley-corn. When these tubes were taken out of the gizzard, several hours after, the bits of flesh extracted from them were found no ways altered either in smell, consistence, weight, or colour.

It is therefore fairly demonstrated, that if the aliment were not comminuted in the gizzard, by grinding, it would not be digested, since no dissolvent exists there, capable of dividing it; and that the comminution it undergoes in the gizzard, equal at least to that of corn in a mill, is entirely owing to the action of that viscus. I do not however ima gine that a simple trituration of aliments, like corn milled, is a perfect digestion: to that, I think, a seasoning of certain liquids is requisite; but I have not now time to explain my idea, much less to recite the facts on which it is founded: nor have I leisure to remove the principal difficulty that has been opposed to trituration, namely, that a stomach which can divide exceeding hard substances, must destroy itself; nor to explain the nature of the seeming callous membrane which lines the gizzard; nor even to say any thing of the gizzard of a species of Indian pigeons, armed with two mills, thought to be stone, but which are really hard horn. I hasten therefore to the experiments I have made on the membranous stomachs of birds, of a texture differing in all respects from that of gizzards.

The partizans of trituration, believing they had sufficiently proved from the texture of a bird's gizzard, that digestion was effected by it, did likewise insist that it was performed purely by the same means, in the stomachs of other animals, even in the simply membranous, as well as in the most fleshy. On the contrary, those who could not be brought to conceive how membranous stomachs could be capable of grinding, would have it, that, in such, a dissolvent was alone sufficient for the business of digestion; and that it was also accomplished the same way in the most fleshy stomachs. It is too common a presumption to imagine the laws of nature

more uniform than they really are: and notwithstanding it has been well proved, that digestion is done by trituration in gizzards, yet it remains to be made appear that it is brought about by the same mechanism in membranous stomachs.

Those of birds of prey are the most proper for affording us information in this matter, especially as they are of the kind nearest in relation to our own. It is true they swallow large morsels at a time, without teeth to chew; in which they differ greatly from the human species. I was therefore desirous of trying them with variously conditioned tubes; and this I was aware I might do without difficulty, and even without taking away the life of any one of these murderers.

Whoever has looked into books of falconry. must know, that carnivorous birds have a faculty of readily rejecting by vomit, any thing that their stomach cannot digest. If they swallow feathers, as they very commonly do, these never digest, nor are they evacuated through the passage of the excrements, but vomited up. I therefore provided myself with a parcel of tin tubes, of about ten lines long, and seven

in bore.

A young buzzard of the largest size, from whom I had plucked some of the quills of his wings to confine him to my garden, was destined to undergo the several trials I judged fit to be made on the carnivorous kind: and the first that was resolved upon was to make him swallow one of the said tubes, open at the ends. Their size rendered them incapable of any great resistance, insomuch that they might be squeezed together by the bare pressure of the finger and thumb. The gizzard of a turkey would not have only flattened such a tube, but broken it into pieces. The buzzard, then confined under a hen coop, vomited it up, after about 24 hours, exactly in the same condition it was swallowed, without the least distinguishable mark of any friction it had undergone. This experiment, which had convinced me, that if the bird's stomach had any force of trituration, it was extremely weak in comparison of that of a gizzard, induced me to satisfy myself forthwith if a dissolvent might not there be employed instead of it. I shall mention the precautions I made use of in order incontestably to prevent decep

tion.

At each end of the tube I fastened a kind of grate, by means whereof the included food was secured from any motion which could possibly be produced in the stomach; so that nothing but a dissolvent could act upon it. All that seemed liable to doubt was, that if a dissolvent did really

reside in the stomach, whether it might not be in too small a quantity for enough of it to get into the tube, so as to act successfully?

The very slender opinion that my first experiment had impressed upon me of a force of pressure in the buzzard's stomach, made me imagine that a grating of fine linen thread might be sufficient for my purpose; and therefore I took a thread, and by applying it according to the length of the tube, wound it round, so that at every turn it passed over the centres of the open ends, and formed meshes, which instead of squares, as usual, were circular sectors, pointed at the centre, and widest at the circumference of the ends of the tube; yet so close there, as not to allow a free passage to any thing more than of half or three quarters of a line in diameter. The turns which formed the grates, and which I call longitudinal, were kept tight with transversal ones which formed a sort of girdle about the middle part of the length of the tube.

The buzzard which I had made to swallow the first tube filled with flesh, and grated at the ends, disgorged it in about 24 hours, without one of the threads being broken or put in the least out of its place, or any of the meshes stretched wider. As soon as I cast my eyes on one end of the tube I was fully convinced of the reality of a dissolvent in this bird's stomach, capable of itself to effect digestion: for at first view, I perceived, within, a very soft greyish white paste, a little of which I took out with a point of a penknife, and squeezing it between my fore finger and thumb found it exceeding tender, resembling the finest clay, moistened to an equal degree. I could observe nothing grumous, nor any diversity of colour or consistence, that had the least resem blance of the fragments of fleshy fibres. Having, by degrees, gotten it all out, I found there was as much as about half filled the tube, and I discovered therein somewhat of a slightly reddish substance, which had rather a more solid consistence than the rest. It surrounded the remains of the bit of beef, and was nearly of the natural colour. The remaining portion of the beef I washed gently to clear it from the reddish paste; and then it did not appear to be above an eighth part of what I had put into the tube.

In making a second experiment I took care to weigh exactly the bit of beef to be inclosed in the tube, which was more than 47, but not quite 48 grains. This tube, which had a grating at the ends, like the first, remained in the buzzard's stomach almost as long again as any of the others; for it was not ejected in less than 44 or 45 hours. The

digestion of the flesh had time to be more completely performed, and I made no doubt of finding it so. Upon cutting the thread and removing the gratings, I looked through the tube, as through a prospect glass, and perceived it to be above half empty throughout the whole length; so that it seemed plain that there could not be so much matter in the cavity, as I had introduced. The greatest part I found to be a whitish grey pap of a much slenderer consistence than the paste of the former experiment. It was indeed liquid, and so far, it is probable, part of it might have escaped through the meshes of the grating.

There was, however, a small portion of the beef remaining under its first form, but of a much paler hue, and not of so firm a consistence. It was parted into three so minute morsels, that being washed and gently drained, and then weighed, they were but six grains, or an eighth of the original. They were so very tender as to manifest an approaching dissolution; for having put them in the palm of my hand, and worked them tenderly with the top of a finger, as with a pestle, they immediately became as a paste.

In both the experiments, the pap, the paste, and the small portion of remaining flesh, had not the least ill scent of tainted meat; they only smelled a little faint, but not at all strong.

It was natural to desire to know how far the power of this dissolvent could exert itself, whose existence had been sufficiently proved; and if it were capable of acting effectually upon bones. Those which I first made trial of were of the softest kind, namely of a chicken a month old, no bigger than a quail. I filled the tube with six pieces, four whereof were of the wings, the other of the thighs, cut to a fit length for the reception. They weighed altogether but 26 grains. The tube being grated as before, I made the buzzard swallow it. It remained in his stomach not more than 24 hours; after which, upon taking off the grating and looking for the bones, I could not perceive the least remains of them. It seemed that they had undergone a quicker and easier digestion than the flesh; for there was nothing left in the tube but a little gelatinous substance, most of which adhered to the inside of one of the gratings.

In another trial I made use of one of the hardest of bones, the rib of an ox; two pieces of which I inclosed in the tube. There was none of the cavernous cellular part about them, but all as compact as ivory, weighing 40 grains. These resisted the dissolvent more than the tender ones had done; for after 24 hours they had lost but 18 grains, or