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cination; that is to say, by the fixation and combination of oxygène.

The effects of the combination of oxygène are equally evident in the vegetable as in the mineral kingdom; and in order to convince our`selves of this, we need only follow the operations in the method of preparing and developing the principal colours, such as indigo, pastel woad, turnsole, &c. We likewise observe, that the first degree of combination of oxygène with oil (in combustion) developes the blue colour for the instant.

. The blue colour is formed in dead vegetables only by fermentation. Now in these cases there is a fixation of oxygène. This oxygène combines with the fecula in indigo, with an extractive principle in turnsole, &c.; and most colours are likewise susceptible of being converted into red by a greater quantity of oxygène. Thus it is that turnsole reddens by exposure to air, or to the action of acids: because the acid is decomposed upon the mucilage, which is the receptacle of the colour; as may be seen in syrup of violets, upon which the acids are decomposed when concentrated. The same thing does not happen when a fecula is saturated with oxygène, and does not admit of the decomposition of the acid. Hence it is that in digo does not become red by acids, but is, on the contrary, soluble in them. It is likewise, for the same reason, that we observe a red colour developed in vegetables in which an acid continually acts, as in the leaves of the oxalis, of the virgin vine, the common sorrel, and the ordinary vine. Hence also it happens, that acids brighten most

of the red colours; and that a very highly charged metallic oxide is used as the mordant for scarlet.

We find the same colours developed in the animal kingdom, by the combination of the same principle. When flesh meat putrifies, the first impression of the oxygène consists in producing a blue colour; whence the blue appearance of mortifications, of flesh becoming putrid, of game too long kept.-This blue colour is succeeded by red, as is observed in the preparation of cheeses, which become covered with amoul. diness at first of a blue colour, but afterwards becoming red.

All the phenomena of the combination of air with the several prin➡ ciples in different proportions may be observed in the flame of bodies actually on fire. This flame is blue when the combustion is slow; red, when stronger and more complete; aud white, when still more perfect.

From the foregoing facts, we may conclude that the blue ray is the weakest, and is consequently reflected by the first combination of oxygène. We may add the following fact to those we have already exhibited. The colour of the atmosphere is blueish, the light of the stars is blue, as M. Mariotte has proved, in the year 1678, by receiving the light of the moon upon white paper: the light of a clear day reflected into the shadeby snow, is of a fine blue, according to the observations of Daniel Major Ephem. des Curios. de la Nature, 1671..

Account of a spinning limax, or slug. By Mr. Thomas Hoy, of GordonCastle, associate of the Linnean So

ciety; from the Transactions of the four feet below the branch from Linnean Society.

T is well known that several in

which it was suspended, and at the distance of four feet and a half from the ground; to which it was ap

Isects, such as spiders and the proaching gradually at the rate of an

caterpillars of many species of moths, can convey themselves safely through the air, without wings, by means of silk lines or threads spun out of their own body: but it has not been observed (as far as I know) that any species, arranged under Linnæus's class of vermes, is possessed of a similar power of self-conveyance. An instance occurred to me, about a year ago, which leaves meno room to doubt but that some of them can convey themselves at least downwards from a considerable height, in that manner. In going through a plantation of Scotch firs, I observed something hanging from abranch of one of them, at a little distance. As it seemed to be larger than any caterpillar of the tribes Geometræ or Tortrices, that I was acquainted with, it attracted my particular notice. When I approached it, I found it to be a snail, or rather slug;* and, at first, supposed that it had been shaken from the tree by wind, after having been entangled in a spider's web, or among the silk lines of some caterpillar. Upon observing it, however, more attentively, it was hanging by one line only, which was attached to its tail. This line or thread, at the distance of one inch and a half from the animal, appeared to be as fine as those spun by the Aranea diadema, but nearer to its body it was thicker; and, at its junction to the tail, was broad and flat, exactly corresponing to the tail itself. The slug was

inch in about three minutes, slower considerably than its ordinary motion, either upon the ground, or even in ascending the trunk of a tree; not so slow, however, as one would expect, if it is considered that a slug is not furnished, like the insects above-mentioned, with a particular reservoir of glutinous liquid, from which the silk lines are spontaneously and almost instantaneously emitted; but that the line, by which it descends, is drawn from that slimy glutinous exudation gradually secreted from its pores, and covering its whole body. It seemed to require a great degree of exertion in the animal to produce a continued supply of this liquid, and to make it flow towards its tail. For this end it alternately pushed out its head, and drew it back again below its shield; turned it as far as possible, first to one side and then to the other, as if thereby to press its sides, and so to promote the secretion. This motion of the head in a horizontal direction to one side, made its whole body turn round; whereby the line by which it hung was necessarily twisted, and from being flat became round. Besides, it might perhaps tend to draw off the glutinous matter, and thus lengthen the line; which could scarcely be effected merely by the weight of the slug, although that was pretty considerable, being between sixteen and seventeen grains.

* Limax.

This slug seemed to be of a species between the Limax agrestis and flavus. Lina. Its specific cha racter might be,

LIMAX (filans) cinereus margine flavo.

uncommon spectacle, which I at first took for a caterpillar hanging by its thread, and reaching to within a foot of the ground, and therefore I did not much regard it; till on a nearer view I perceived it, to my abour three quarters of an inch in great surprize, to be a small slug, length. It hung by the extremity of its tail, and gradually descended till it almost touched the ground, when I shook it off with my finger. The thread seemed to issue from the body of the animal; yet I never observed asecond or a former instance of any kind of snail having the fa culty of forming a thread.

Perhaps the shade of the fir-trees, and the wet foggy weather, when I observed it, may have rendered the Limax flavus of a paler colour; therefore I cannot pretend absolutely to introduce this, as a new species, to the acquaintance of the Linnean Society. But if the foregoing account exhibits a new instinct, or something that has not been heretofore observed in the animal economy, it may perhaps not be below the notice of a society February 6, 1791." instituted for promoting the knowledge of natural history.

ADDITIONAL NOTE,
By Dr. Shaw.

It is considerably more than ten years since I had an opportunity of observing the phenomenon so ac curately described by Mr. Hoy. Having never, either before or since, observed a similar appearence, I

cumstance merely accidental; but as it is thus confirmed by Mr. Hoy, there seems no reason to doubt that the animals of the genus Limax have a power of occasionally managing their glutinous excretion in such a manner as to serve the purpose of a thread in a direct descent.

The copy of my own memorandum on this subject is as follows:

September 27, 1776, Sitting in an arbour, about eight feet high, I was amused with a very

"GEORGE SHAW.

Case of hydrophobia; with the appearances on dissection. Communicated in a letter to Samuel Foart Simmons, M. D. F. R.S. by John Ferriar, M.D.physician to the in firmary at Manchester; from Me dical Facts and Observations.

N Friday morning, December

John Johnson, recommended as a home patient of the infirmary, who was said to have been bitten by a mad dog.

I found him in a tremulous ir ritable state, with a weak irregular pulse, and a white tongue. His eyes looked wildly; he was fearful of every unexpected noise, and seemed to be continually on the watch against surprises. When interrogated respecting his complaints, he gave a long detail of pains in his chest, cough, and difficulty of breathing ;but was unwilling to mention his dread of water. He owned

that

that, a considerable time before, he had been bitten in the left cheek by a strange dog, which leaped at his face in passing while he was at work in the street. The accident affected him so little, that the precise date of it had escaped his memory. He guessed it to have happened more than three months ago. Since that time he had been twice afflicted with complaints supposed to be pleuritic, which were removed by bleeding, blistering, and otherremedies, of which he could give no account. He had been bled twice within the last week, and had a blister on the left side of the chest when I saw him.

On Monday, November the 29th, in the evening, his wife had observed, for the first time, that he swallowed some gin and water with reluctance and difficulty; the uneasiness in swallowing liquids soon became his principal complaint, but the bite was not recollected till Thursday evening; when a medical gentleman, who was applied to, inquired whether he had ever been bitten by a dog. Even then he recollected the circumstances but imperfectly. He got down solids with great ease during the whole complaint.

When I desired him to drink a little water, he shewed strong marks of disgust, but, recollecting himself, said he would try; that he did not believe the dog to have been mad, (an idea in which I encouraged him) and that he was not afraid of water. As soon as he touched the cup, I perceived some spasmodic contractions of the muscles of deglutition, and when he raised it towards his mouth the muscles of the cheeks were strongly contracted, and a sort of convulsive gulping was very fre

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quently repeated. After one or two unsuccessful attempts, he swallowed a small quantity of water, but with a violent struggle, succeeded by universal tension; and he would not be persuaded to make another trial.

He complained that cold air affected his throat with a similar uneasiness; and when asked where the impression was felt, pointed to his throat, immediately under the thyroid cartilage. The opening of the door always made him complain.

His discourse was somewhat incoherent, and he frequently refered, with some degree of terror, to the circumstance of the bite.

By his wife's account, he had been a sober industrious man; abstemious with respect to food; and addicted to no practices likely to pervert his imagination. His age was thirty nine; his evacuations were in a natural state.

The scar on his cheek, which was between the ear and the angle of the jaw, but rather more advanced, was hardly discernible : his wife remembered to have seen it bloody. I had him removed to the hospital as soon as possible, that he might enjoy every advantage of attendance: and till I could have the satisfaction of consulting with my brethren, ordered him to take a bo lus, containing a scruple of bark, six grains of musk, and half a grain of opium: he was immersed in the cold bath: and was directed to swallow, as

often as possible, a portion of a mixture of vinegar and water.

After his removal, as his wife had informed me that the sound of water distressed him, I directed some to be poured out in the passage adjoining to his room. He started at the noise, looked wildly round, begged

to

to be sent home, and said he was not afraid of water.

At five o'clock in the afternoon we met in consultation, when the horror of water, and difficulty of swallowing it, were ascertained in presenc of all the physicians to the house.

We agreed to scarify the cicatrix on the cheek deeply, and to apply a blister over the incisions: a bolus, containing a scruple of bark, fifteen grains of musk, and two grains of opium, was directed to be given every four hours; two drachms of strong mercurial ointment were applied to the throat, arms, and groins; amixture of eight ounces of distilled vinegar, and twelve ounces of decoction of bark, was ordered, of which three or four table-spoonsful were to be given as frequently as possible; and a poultice, consisting of three drachms of galbanum, two scruples of opium, and one drachm of camphor, was applied, after the mercurial friction to the throat.

About nine o'clock the same even ing I saw him again. He had swallowed his medicines without much reluctance, but was more incoherent, and complained greatly of cold,

During the night his delirium increased: he was very restless, impatient, and intractable. He threw himself out of bed repeatedly, and with his nails scratched the hand of one of the keepers who attemped to replace him. However, he took four boluses, and swallowed more than a pint of his mixture. He had one stool before morning.

At nine o'clock on Saturday morning, December 4th, we met again in consultation. We found that his difficulty in swallowing liquids was less he had taken some very thin

:

porridge, the usual breakfast of the house; and hedrank several draughts of his mixture without any striking appearance of disgust, in our presence; but his eyes were heavy, and inclined to fix, his pulse much sunk and there was a constant tendency to low delirium. We therefore concluded that the termination of the disease approached:but directed that the plan we had agreed on should be pursued as long as he should be capable of swallowing. Before I left him he retched several times, and brought off some wind: half a grain of emetic tartar was directed to be added to his next bolus, but he did not live to take it. At a quarter past ten he swallowed some of his mixture, and immediately after threw up a part of it again. He then fell into convulsions, and died in the course of a few minutes.

I was very desirous of examining the body as early as possible, that the appearances attending this dreadful disorder might be fairly ascer tained; the inflamation of the stomach, described in former dissec. tions, having been often attributed to the action of the gastric juice. Accordingly, the body was opened by Mr Simmons, at a quarter before three o'clock on Saturday afternoon, in presence of most of the physicians and surgeons of the hospital.

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In the brain, which was the part first examined the only preternatural appearance was a distention of the pia mater, on both hemispheres, with a limpid fluid. The quantity of water in the lateral ventricles, at the basis of the brain and round the spinal marrow, appeared to be somewhat unusual. The lungs were uncommonly sound, excepting one

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