Dr. Jackson's teftimony in favour of bleeding 495 An account of Sydenham's practice, and his reasoning, 495–504 A curious critique on Sydenham, by his tranflator ....... Offweating......... 501, 502 505-508 ib. 517 517, 518 Of other ftimuli, as opium, ether, and wine When we should encrease the quantity of wine ..... Of the conduct of the patient upon the ceffation of the fever SECT. II.. OF TEMPORARY EXHAUSTION. Juft as the morning fteals upon the night, That now lies foul and muddy. SHAKESPEARE. To fhew the diminution of fenfibility from increased action, if one hand be put into very warm water, and then immerfed with the other into fubtepid water, to the former this water will appear extremely cold, while to the other hand it will impart an agreeable warmth For the fame reafon we feel a chillnefs on coming into an atmosphere of a temperate warmth, after having been for fome time in a very close apartment. Hence we are unable clearly to diftinguish objects, immediately after we have feen a bright flash of lightning pervade the gloom of night. Thus MILTON, in defcribing the light and glory which flows from the divine prefence and the majefty of GOD, fays, Dark with exceffive light thy fkirts appear. Here is an idea not only practical in an high degree, but strictly and philofophically juft. Extreme light, light, by overcoming the organs of fight, obliterate all objects, fo as in its effects exactly to resemble darkness. Thus, after having looked at the fetting fun for a fhort time, if we turn our eyes to a lefs fplendid part of the heaven, a dark spot will be perceived exactly refembling the shape of that bright luminary. That thefe phænomena depend upon the exhauftion of fenfibility, may be proved alfo by looking ftedfaftly on an area of fearlet filk of about an inch diameter spread on white paper, the fcarlet colour will gradually become fainter, until it entirely vanishes, if the eye be kept uniformly upon it. Or if you look at a furface of light blue, and then place upon it a smaller furface painted of the ultramarine blue, the appearance of the light blue will be nearly obliterated. It is on this account that painters put in their first shades darker than a bye-stander ignorant of this law would imagine right, and produce the greateft effect by the contraft of shades. SECT, SECT. III. OF ASPHYXIA FROM MENTAL AGITATION. -Ubi vehementi magis eft percuffa metu mens, LUCRETIUS. IN exceffive fright the eyes for a moment flash fire; the hair becomes electric and ftands erect; the heart palpitates; the body is thrown into the attitude for escaping; but the danger being inevitable, cold fweats fucceed; the hair of the body droops; the eyes become dim, and as it were femipellucid; the furface flaccid, cold, and pale; and the perfon finks down inanimate. Admitting the analogy, if not perfect identity betwixt the nervous fluid and that of electricity*, we * Sir ISAAC NEWTON, at the end of his Principia, has the following Query: "Is not all fenfation performed, and the "limbs of animals moved, in a voluntary manner by the power " of a certain fubtle fluid, resembling ELECTRICITY, which "we will call ether, i. e. by the vibratory motion of this spirit "-propagated along the nerves from the external organs of the fenfes To the BRAIN; and FROM the BRAIN into the mufcles." "If a man in the dark," continues Sir ISAAC NEWTON,"preffes against the corner of his eye, or receives "a blow, as he turns away his eye haftily from the injury, he "will perceive a circle of colours, or a flash of light, and this "appearance will continue about a fecond of time." Vide bis OPTICS, Qu. 16. It was before obferved, that if a plate of |