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 the length of the tube.

of

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

about half their weight. Each bone had a small drop of gelatinous matter at either end, being doubtless part of the substance which had been dissolved. That which remained under the form of bone, was hard; and these two fragments were not entirely dissolved, that is, they were not reduced to less than four grains, after having been twice more introduced into the bird's stomach.

The true carnivorous birds, such as our buzzard, feed only on the flesh of other birds, and that of quadrupeds and reptiles: no degree of hunger will induce them to swallow grain of any kind. Is this because the dissolvent of their stomachs can act only upon flesh and bones, and not upon vegetable productions? Nature has taught animals infallible lessons, such as they most stand in need of, and which they never omit to pursue. It was reasonable therefore to presume, and curious to be satisfied, that this dissolvent in the buzzard's stomach, of such efficacy upon flesh and bones, would fail upon substances of the vegetable kingdom. I have already related an experiment, several times repeated, which seems to prove it. The thread gratings of our tubes always remained entire, without damage to any single twist.

The tubes, however, indicated very easy means of proving the power of the dissolvent on vegetable substances, which seemed less capable of opposing it, than strong and dry fibres of plants. I gave several tubes, filled with corns of wheat and barley, to the buzzard, both in the husk and without it, and also boiled. In others I put a bit of the crumb of bread, as long as the tube, and stuck with different grains; and lastly, one half of another tube was filled with Hesh, and the other half with corn. None of these experiments discovered the least alteration in any one grain of corn by the dissolvent. All came out as they were put in, saving a little swelling, such as would have been from a like continuance in any damp place. The crumb of bread seemed to have been a little operated upon, as though it had been chewed, but it was not converted to a paste, as the flesh was, that was included along with the grain.

I have reason to think that the dissolvent can operate but little more on fruit than on grain. A piece of ripe orange pear weighing 29 grains, after remaining 24 hours in the buzzard's stomach, came out unaltered; appearing only a little macerated from the warmth it was confined in. It tasted somewhat aigre and had lost only four grains of its weight.

Now what must be the nature of this liquor, which has the like power on flesh and bones as aqua regia on gold; and

VOL. II.

F f

can do no more with vegetables, than that menstruum can do with silver? We can scarcely hope to procure enough of this dissolving liquor to furnish a sufficient variety of trials to discover its several properties; but our tubes which have stood us so much in stead in examining into the affair of digestion, so far can supply us as to furnish proof enough of its nature. If a tube were filled with a sponge, a substance which no bird of prey feeds upon, and which, from what has appeared above, his stomach cannot digest; it should seem probable that it would imbibe the dissolvent. In short, I introduced several bits into a tube, taking care not to press them too close together, and grated up the ends. These the buzzard swallowed, and rejected as usual. The sponge, before it was put in, weighed only 13 grains; but taken out of the tube it weighed 63. Here then were 50 grains of the liquor, which I could easily squeeze into a vessel proper for keeping it. This experiment suffices to shew that we may become masters of a considerable quantity of it. A buzzard may be made to swallow two or three tubes filled with sponge in a day. But if, instead of a buzzard, the thing were to be done by a vulture or eagle, it might not be difficult to obtain a good glass-full of the dissolvent.

1753, July, Aug. and Sept.

DE REAUMUR.

XIV. The Cause of the Lustre or Resplendency of the Sea-water in the Night time, discovered and explained.

THE splendour of the sea water during the night, has long been a subject of admiration, and upon the coasts in the neighbourhood of the town of Chioggia, it is particularly remarkable: at first sight one would imagine that the brilliant images of the fixed stars were reflected by the sea, and when the sea is agitated by winds, or pierced by the strokes of oars, this brightness becomes much more vivid and copious, especially in places abounding with the alga marina, or sea weed. This beautiful phenomenon, which continues in our parts, from the beginning of summer till autumn, hath often engaged my attention, and at length excited an earnest desire to discover, if possible, the true cause of it.

One fine summer night I walked out upon the sea-shore, and after having observed this shining water for some time, I took a vessel full of it home with me. I placed it in a dark room, and observed, that as often as I disturbed and agitated the water with my hand, a very bright light issued from it.