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wholly produced by the concave bright-coloured surface of the tapetum, collecting the rays of the external light, concentrated by the cornea and crystalline lens, and reflecting them through the pupil. When the iris is completely open, the degree of brilliancy is the greatest; but, when the iris is partly contracted, which it always is when the external light is increased, then the illumination is more obscure, and appears to come from the iris; a part of the right reflected from the tapetum being thrown back, by the concave surface of the cornea, upon the anterior surface of the iris, giving it a light shining appearance. The influence which the will of the animal has over this luminous appearance, seems altogether to depend on the contraction and relaxation of the iris. When the animal is alarmed er first disturbed, it naturally dilates the pupil, and the eye glares; when it is appeased or composed, the pupil contracts, and the light in the eye is no longer seen.

The most material information that has been gained in this investigation, is the transparent state of the retina in the eye during life; the opaque membraneous appearance which it puts on in the dead body not being natural to it, but a change which takes place in consequence of death. This fact is almost all that is necessary to explain the luminous appearance in the eyes of cats.'

Having ascertained the transparency of the retina, when the eye is examined in a recent state, the author proceeded to investigate the internal structure of the optic nerve, and to determine whether this was also transparent in the same state. For this purpose,

The posterior half of a cat's eye, while in a very recent state, was immersed in a bason of water, and examined. The tapetum appeared very bright, the retina not having acquired sufficient opacity to become visible: the entrance of the optic nerve was a very white spot, which seemed to be opaque: but, when small pieces of coloured paper were alternately placed between the outside of the eye and the bottom of the bason, their colour was distinctly seen in the cavity of the eye, through the substance of the optic nerve; so that, at this part, the internal structure of the nerve has a degree of transpa rency.'

This fact being discovered led to the examination of its substance by means of magnifying glasses. The microscope used for this purpose was a single one, magnifying about 23 times; and the experiments were afterward repeated with a double microscope, which magnified the object about 40 times. The optic nerve of the horse was selected, and it was examined in a very recent state. In the first experiments, a transverse section of the nerve, near to its termination in the eye, was placed on glass, and exhibited in the microscope the following appearances: it was evidently composed of two parts; one opaque, the other transparent. The opaque portions were nearly circular in their shape, about 600 in number, and touched

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touched one another; the interstices between them were transparent.' The opaque parts were composed of a great number of smaller portions, which were also opaque,

The next object was to determine whether the nerve had the same structure in its whole course. With this view, transverse sections in different parts of the nerve were examined; and the nerve was found to be composed of the same substances, though the size and number of the opaque parts differed very much. The structure of the nerve in a longitudinal direction was afterward examined by removing a part of the coat, formed by the dura mater, together with a thin vascular membrane which lines it, from a portion of the nervous pulp, for about one inch in length; and then observing the external surface of the pulp with a magnifying glass. The structure was evidently fasciculated, but the fasciculi did not run parallel to one another. They seemed to unite together and separate again, in such a manner that any one of them could not be traced for half an inch in length, without being lost in the neighbouring part.' The fasciculi were largest in that part of the nerve which was near to the brain, and smallest towards the eye; and they appeared, after repeated observation, to be continued fibres.

From the experiments recited in this paper, it appears that the internal structure of the optic nerve is formed in the following manner:

At its origin from the brain, it consists of 30 or 40 fasciculi or bundles of extremely small opaque pulpy fibres, the interstices between which are filled with a transparent jelly. As the nerve goes farther from the brain, the fasciculi form smaller ones, of different sizes. This is not done by a regular sub-division, but by a few fibres going off laterally from several large fasciculi, and being united, forming a smaller one: some of the fasciculi so formed, which are very small, unite again into one. In this way, the fasciculi gradually diminish in size, and increase in number, till they terminate in the retina, Near the eye, where the fasciculi are most numerous, the substance of the nerve has a considerable degree of transparency, from the number of transparent interstices between them; but this is less the case nearer the brain, where the interstices are fewer.'

Similar experiments were made on the internal substance of the fifth and seventh pair of nerves, near to their origin at the brain; and their structure was found to be the same.

On the whole, these experiments shew that

The nerves do not consist of tubes conveying a fluid, but of fibres of a peculiar kind, different from every thing else in the body with which we are acquainted. The course of these fibres is very curious; they appear to be constantly passing from one fasciculus to another, so as to connect all the different fasciculi together by a mixture of

fibres.

fibres. This is different from the course of blood-vessels, lymphatics, or muscular fibres; the only thing similar to it is in the formation of nervous plexuses, which leads to the idea of its answering an essential purpose, respecting the functions of the nerves.'

On the Decomposition of the Acid of Borax, or Sedative Salt. By Lawrence de Crell, M.D. F.R.S. Translated from the German.

The experiments here recited will probably attract the attention of the theoretical and practical chemist. The subject is curious: Dr. C. has already taken great pains in the investigation of it; and he is prosecuting his inquiries with singular assiduity. We have before us an account, very much in detail, of 66 experiments, which were instituted with a view of ascertaining the nature and properties of this sedative salt; and the author announces his intention of communicating many others, which he has actually made, as soon as they have been sufficiently repeated. Conceiving that this acid is contained within some unknown species of earth, intimately combined; or within some sort of inflammable matter; or that, according to a phrase used in the new system, there might be a deficiency of acid matter,' he was naturally led to select some more powerful acid, which would probably separate and dissolve the earthy particles, destroy or change the inflammable matter, or impart the acid it might be supposed to want.' The parti cular acid which Dr. C. imagined would best answer his purpose, and of which he made use, was the oxygenated muriatic acid, prepared with manganese; and he pursued his analysis, in the application of this menstruum, by a gentle, long-continued, digestive heat, and by a repeated distillation of the same menstruum in preference to a heat which is more violent, and which operates more quickly. On his various processes we shall not now enlarge: but we must observe, in general, that his experiments are well adapted to evince the decomposition of sedative salt, and to shew that one of its component parts is inflammable matter, which may be converted into coal.

• Every other substance (he says) liable to be changed into coal, (as gum, tartar, sugar, &c.) suffers this change by a gentle heat, and deflagrates with nitre, in the degree of heat necessary to melt the former. But sedative salt can bear a red heat for many hours, without shewing any signs of becoming coal, of burning, or of deflagra tion. Astonishing phænomenon! What menstruum preserves it so securely against the assault of force, in a dissolved state, and yet suffers itself to be separated from it by more gentle means? What power exists here to protect the inflammable particles (which afterwards turn to coal) so effectually against a degree of heat which nothing else can resist? Of what nature is the salt obtained in con

junction

junction with the coal? These are all questions which excite great interest, but which are not easily answered.'

The author's success in resolving them will appear in some of his future communications.

To the class of Philosophical Papers we may refer the customary Abstract of a Register of the Barometer, Thermometer, and Rain, at Lyndon in Rutland, 1797; with some Remarks on the Recovery of injured Trees. By Thomas Barker, Esq. Also the Meteorological Journal, kept at the apartments of the Royal Society, which terminates this volume.

NATURAL HISTORY, &c.

Observations on the Manners, Habits, and Natural History of the Elephant. By John Curse, Esq.

By a residence of more than ten years in a province of Bengal, where herds of elephants are taken every season, and by having the elephant-hunters for five years under his absolute direction, Mr. Corse is peculiarly qualified to render the subject of this paper instructive and interesting. He seems also to have been attentive and assiduous in availing himself of the opportunities which his situation afforded, for prosecuting experiments that would enable him to detect the errors of European writers, and to discover many particulars in the history of the elephant that were not formerly known. The experiments and observations contained in this paper form a sequel to those which were communicated to the Asiatic Society in the year1789, on the methods then used for taking and training wild elephants, and which were published in the 3d volume of the Researches of that Society. By Mr. C.'s account, it appears that elephants attain their full size between 18 and 24 years of age. Their height has been much exaggerated. In India, the height of females is in general from seven to eight feet; and that of males from eight to ten feet, measured at the shoulder. The sagacity and memory of these animals have been wonderfully extolled; and it has been said that, after having once received an injury, or after having escaped from confinement, it is not possible by any art again to entrap them :-but the present author recites several instances which' disprove this assertion. It has been also said that tame elephants would not breed: but the experiments here recited (with a de gree of minuteness which delicacy will not allow us to repeat) prove the contrary fact. Their period of gestation is about 20 months and eighteen days. Many circumstances are related with regard to the mutual intercourse of these animals, and the method of rearing their young; which, though of no great im-: portance to our readers, may be of service in particular circum

stances,

stances, and may possibly suggest a method of improving the breed of elephants in size, strength, and activity.

On a Submarine Forest, on the East Coast of England. By Joseph Correa de Serra, LL.D. F.R.S. & A.S.

The forest described in this paper is situated near Sutton, on the coast of Lincolnshire. It consists of a number of islets of moor, visible only in the lowest ebbs of the year, and chiefly composed of decayed trees, which extend at least twelve miles in length, and about a mile in breadth. They form, however, only a part of a very extensive subterraneous stratum, which has been traced as far as Peterborough, (more than 60 miles to the south of Sutton,) and which reaches, on the north side, as far as Grimsby, on the south side of the mouth of the Humber. Many circumstances are noticed, which ascertain the identity of those widely-extended tracts that exhibit tokens of decayed trees; and which, in some distant period, have been stripped of their covering of soil by an irruption of the sea. The islets, examined by Dr. Correa, in company with the President of the Royal Society, consisted almost entirely of roots, trunks, branches, or leaves of trees and shrubs, intermixed with some leaves of aquatic plants.

The remains of some of these trees were still standing on their roots; while the trunks of the greater part lay scattered on the ground, in every possible direction. The bark of the trees and roots appeared generally as fresh as when they were growing; in that of the birches particularly, of which a great quantity was found, even the thin silvery membranes of the outer skin were discernible. The timber of all kinds, on the contrary, was decomposed and soft, in the greatest part of the trees; in some, however, it was firm, especially in the knots. The people of the country have often found among them very sound pieces of timber, fit to be employed for several œconomical purposes. The sorts of wood which are still distinguish able are birch, fir, and oak. Other woods evidently exist in these islets, of some of which we found the leaves in the soil.'

The soil, in which these trees grew, is a soft greasy clay : but it is composed, for many inches above its surface, of rotten leaves; some of which belonged to the Ilex Aquifolium, and others to some species of willow.

After a description of the vegetable ruins which are the subject of this paper, the author proceeds to inquire what is the epoch of the destruction to which they are owing, and by what agency it was effected. Many instances are recited, in which a force of subsidence, the natural consequence of gravity, operating slowly though constantly, and aided by extraneous causes, has produced similar effects.

This force, (says the author,) suddenly acting by means of some

earthquake,

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