appearances; the ligature of the nerve, or the interception of its communication with the brain, hindering it to tranfmit to it its vibrations. But it is now well proved, that this opinion, on the nature of the nerves, cannot be maintained; the nerves, far from being claftic, being of a very foft fubftance. A great number of other facts ftill prove, that, when a motion is excited in a mufcle, it is by the paffing, in this mufcle, of a certain fubftance, of a certain fluid contained in the nerve and that this fluid comes from the brain; that this organ is the refervoir of it; and that it is there prepared, many facts, both of anatomy and phyfic, ftill evince it to be fo. There are numerous experiments which prove that, the brain being obftructed, inflamed, cut, or in fuppuration, fometimes the motion is weakened or destroy. ed; fometimes the feeling, and often both happen at once. Anatomy and injections feem, with equal certainty, to prove that the brain is a fecretory organ, as feveral other organs; and, when examined with attention, one cannot help finding in it a very great refemblance to the kidney. This excretory organ is compofed only of two fubftances, the cortical fubftance and the tubulous; the brain has only two likewife, the cortical fubftance and the medullary. In the kidneys, the cortical fubftance gives birth to the tubulous; in the brain, the cortical fubftance gives birth to the medullary; the tubu. lous fubftance is feen to arife in the kidney from all the points of the cortical fubftance; in like manner it is obfervable in the brain, that the medullary fubftance comes from VOL. IX.

all the points of the cortical; laft ly, if in the kidneys the different portions of the tubulous fubftance, difperfed here and there, appear to chufe for themfelves, as it were, an origin, and afterwards to affemble as fo many convergent rays for forming papille; the different portions of the medullary fubftance are feen alfo to affemble, and become convergent, for forming the three nervous cords or strings.

So ftriking an analogy in the difpofitions of parts, feems to indi. cate one as great in the functions; confequently, if in the kidney there is a fecretion of urine in the cortical fubftance, it. feems there fhould be performed, in like man. ner, a fecretion of a fluid, or spirits, in the cortical fubftance of the brain; and likewife, if the tubulous fubftance receives the liquor continually filtrated by the cortical fubftance, the medullary fubftance of the brain ought to receive the fpirits filtrated by the fubftance of the brain, but with this difference, that they ought to pafs from that fubftance into the nerves, to return afterwards to the brain; whereas the liquor filtrated by the kidney, ought no more to enter into it. If we add to this, what the ftructure of the brain informs us of, it will appear to refult therefrom, that the red part of the blood circulates in the arteries, and in the red veins of the pia mater; that the cortical fubftance, being compofed of an infinity of minute arteries and veins, which are proceffes of those of the pia mater, there will circu late in thofe arteries a fluid, by far finer and thinner than the red part of the blood; that thofe minute arteries and veins continuing with the fubftance of the nerves, the fi

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laments of that fubftance will be arteries, fuch as thofe of the cortical fubftance; in fine, as the tenuity of those venules is always increafing, in like manner thofe of the medullary fubftance ought to be by far ftill more minute; and, if we cannot perceive them, it is because our fenfes are too weak, but they do not therefore exift the lefs.

M. Bertin concludes from thence, that the red part of the blood, brought to the brain, circulates in the pia mater; that fluids, more attenuated and more tranfparent, circulate in the arteries and venules of the cortical fubftance; and laftly, that ftill more fubtile fluids pafs into the fubftance of the nerves, which are only minute arteries and veins, through which those fluids, or fpirits, flow from the brain to the extremities, and return from the extremities to the brain. Thefe fpirits are diftinguifhed into three different claffes, not by any difference obferved or obfervable in their nature, but by that of the functions attributed to them; the first are the vital fpirits, which animate the muscles of the parts effential to life; the fecond are the natural fpirits, that animate the mufcles which have a more diftant relation to life; the motion of those two forts of fpirits does not obey the command of the will, or at least we cannot exercise it in regard to them; the third are the animal fpirits that ferve for the functions of the foul and body: they are diftinguished into two forts, the animal moving fpirits, and the fenfitive animal fpirits; the first are thofe, which, in confequence of the action of the will, animate out mufcles; the fecond,

or the fenfitive fpirits, are thofe which convey to the brain the impreffions of objects.

Such is the picture M. Bertin gives us of the means which nature has employed for producing and circulating this fubtile fluid; thofe fpirits which, diffused throughout the body, animate it, give it all its motions, and make it fenfible of the impreffion of objects; but the part of this fyftem, which regards the caufe of our motions and fenfa tions, and feems to be now adopted by the best phyfiologifts, is not the work of the moderns, but we are indebted to Galen for it. This great man, fays M. Bertin, saw very well, upwards of 1600 years ago, that a fluid ought to produce all the wonderful effects which we observe in the exercise of our mo tions and fenfations; and be derived its fource from the brain, from whence it diffufed itself thro❞ the rest of the body. If he could not see what modern anatomy has difcovered, he could ftill less fee thofe fpirits, that fubtile fluid; but he conjectured from all the effects he had obferved, that things must be as he explained them; and thus he began to take off a corner of the veil that hides from us the myftery of our fenfations. The moderns have found new proofs of his opinion, but have not made a greater progrefs than he did in regard to the courfe and circulation of the nervous guid, or the fubtile fluid that animates us. Nature acts always, in her operations, by the fame principles; and if the makes the blood to circulate, for nourishing and maintaining all the parts of the body, and hindering it to be altered by the reft, in like manner the makes the nervous fluid ད་

their wells, and that fuch was the cause of their death. Befides, he pretends to affirm, from the little experience he had of the plague, that the fame perfon cannot have it twice, which is abfolutely falfe. The Greek Padre, who took care of the Greek hofpital at Smyrna for fifty years, affured me, that he had the plague twelve different times in that interval; and it is very certain that he died of it in 1736. Monfieur Broffard had it in the year 1745, when he returned from France; and it is very well known that he and all his family died of it in April 1762. The Abbé, who takes care of the Frank hospital at Pera, fwore to me the other day, that he has had it al ready, here and at Smyrna, four different times. But what is ftill more extraordinary, is, that a young woman, who had it in September laft, with its moft pathognomonic fymptoms, as buboes and carbuncles, after a feve, had it again on the 11th of April, and died of it fome days ago, while there is not the leaft furmife of any accident in or about Conantinople fince December, this only one excepted: but there died four perfons in the fame little houfe in September; and, as the houfe was never well cleaned, and this young woman always lived in it, fhe was at laft attacked a fecond time, and died.

The only antecedents that I could cbferve to this malady, were a great murrain among the black cattle in May 1745; and in the beginning of June, the fame year, fwarms of butterflies flew about, and there were great numbers of caterpillars creeping every where,

and afterwards a violent plague and, after obferving the fame anno 1752 and 1758, you may recollec that I foretold to you, Sir, that we fhould have a hot plague in those years; which accordingly happen ed, especially in the months of Auguft and September 1758, when many of Marfellina's family, Spathari, Skwack him's cook, Charlacci Rimbeault, Jackino's son, &c. died of it.

The plague is now more frequent in the Levant than it was when I came first into this country, about 30 years ago; for then they were almoft ftrangers to it in Aleppo and in Tripoli of Syria, and they had it but feldom at Smyrna; whereas now they have it frequently at Aleppo, and fummer and winter at Smyrna, though never fo violently in the winter; which muft be owing to the great communication by commerce over all the Levant, and more extended into the country-villages than it used to be. I take the plague to be an infection communicated by contact from one body to another; that is, to a found body from an infected one, whose poifonous effluvia, fubtile miafmata, and volatile fteams, enter the cutaneous pores of found perfons within their reach, or mix with the air which they draw in refpiration, and, fo advancing by the vafa inhalantia, mix with the blood and animal fluids, in which, by their noxious and active qualities, they increase their motion and velocity, and in fome days pro duce a fever; fo that the nearer and the more frequent the contact is, the greater is the danger, as the noxious particles, exhaling from the infected perfon, muft be

more:

more numerous, and confequently have greater force and activity in proportion to their distance.

Some perfons are of opinion, that the air must be infected, and that it is the principal cause of thefe plagues; whereas I prefume, that the ambient air is not otherwife concerned, than as the vehicle which conveys the venomous par ticles from one body into another; at leaft in fuch plagues as I have feen hitherto at Smyrna and Conftantinople; allowing always, that the different conftitution of the air contributes very much to propagate the plague for the hot air dilates and renders more volatile and active the venomous teams, whereas cold air contracts and mor tifies them. The perfon having the plague may be faid to have a contagious and poisonous air in his room and about him, while at the fame time the open air is free from any dangerous exhalations; fo that I never was afraid to go into any large houfe, wherein a plaguy perfon lived, provided that he was confined to one room.

The peftilential fever thews itfelf first by a chilliness and shiverings, even in the months of July and Auguft, fo very like the firit approaches of an ague, that it is impoffible to diftinguish the one from the other at first fight. This cold fit is foon accompanied with a loathing naufea and defire of vomiting, which obliges the patient at laft to discharge a vast quantity of bilious matter, with great uneafinefs and oppreffion in the tho rax and mouth of the ftomach, attended fometimes with a dry cough, as in an intermitting fever; and even in this ftage it is very difficult to diftinguish the one from the

other. Next, the patient has a violent headach and giddiness, with fome flight convulfive motions; he breathes hard; his breath and sweat flink; his eyes are ruddy; he icoks frighted, fad, and pale; he has an infatiable thirft; his tongue is yellowish, with a red border; he has a total lofs of appetite, reftlefinefs, great inward heat, and more than could be expected from the fever, which is fometimes pretty moderate, but grows ftronger frequently towards night: the patient very often bleeds at the nofe. He continues in that difmal condition for fome days, until the venomous matter begins to be feparated in fome meafure from the blood, and difcharge itself critically upon the furface by the cutaneous eruptions of buboes, carbuncles, blains, petechial fpots, and fome fmall veficles or blifters; but all these fymptoms are not to be looked for in the fame perfon. When the cutaneous eruptions appear, and grow fenfibly, the patient finds himself better, and fomewhat relieved from the great op preffion he laboured under before, Some perfons in the above state have a very violent fever, fometimes attended with a delirium and phrenfy; others are ftupid, fleepy, and complain of nothing. Such as are furious and delirious feldom live fo long as they who are fleepy and ftupid; but, if they live long enough to have the cutaneous eruptions pufh plentifully, and their phrenfy begins to abate after wards, they may recover more probably than fuch as are fleepy and have a moderate fever; though I have known fome of them likewife die.

I make no doubt, Sir,

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but you