Pagina-afbeeldingen
PDF
ePub
[ocr errors]

longer useful in the general system, as organized bodies; and it is then absolutely necessary, that their frame should be diffolv. ed, and their elementary principles dispersed, in order to furni nourishment for those beings that yet continue to live.'

The commutation, therefore, of this principle of cohesion, when in its fixed and strongly attracting ftate, into that of its proving a cause of their diffolution, in its elastic and repellent one, really being, as our Author fupposes, not easily comprehended, he has judged it expedient to add to such proofs of it, as had been already published, a new set of experiments, from which he proposed to obtain additional light, in some points of very great importance in the animal oeconomy. The number of experiments in this Essay are thirty-four.' The first feven were made in order to discover the relative quantity of air set free from different mixtures by fermentation; and do allo fhew, what different alimentary mixtures or substances were disposed to ferment sooner or later than others, in the same degree of heat. The eighth experiment lhews the perfect sweetening a bit of putrid mutton, impregnated with the vapour of fermenting wort. The ninth, (which includes a very ingenious and conclusive experiment of Dr. Black's) shews the method of transferring air, from an effervescent mixture, into another substance, adapted to receive and to fix it; and which having been before deprived of its former air, was, until transferring this, incapable of effervescence, which is thus restored to it. The contrivance for effecting this, which is at once very simple and effectual, is rendered perfectly clear by an engraving.

The tenth experiment compares the fermentative power of the Saliva and the Bile; the first of which fermented two hours fooner than the last, tho' the fermentation of this continued twice as long, and was still brisker than that of the fpittle. The eleventh and twelfth are intended to enforce the eighteenth of Dr. Pringle's experiments; and prove, that bodies in a state of putrefaction are exciting ferments to such as are sweet; which fact has been supposed to obtain in carivus teeth, &c.

The thirteenth was inftituted to prove the fermentative power of the Bark, on which Mr. Macbride supposes its efficacy greatly to depend: but this experiment seems somewhat lefs conclusive to us, as the first signs of the fermentation of the Bark, with the addition of human faliva, quickly disappeared, and was perfectly at rest eighteen hours after, tho' it had remained for fix hours in a moderate heat, being suffered to cool the last twelve. Neither did any motion revive in this mixture, till full twenty hours after the addition of ox-gall, which at length appeared even in the cold; but, on the application of moderate heat, the ; U 2

fermentation

fermentation returned very briskly, continuing fo for twentyfour hours, and throwing off great quantities of air. To be ingenuous, we acknowlege this attempt to account for the efficacy of the Bark from its fermentation, (especially when that occurred to it with more than usual flowness and difficulty) favoured to us of a common disposition to account for plain effects by fome favourite theory, which sometimes strains very hard to reconcile thein to it: since the styp:icity of the Bark, and of its resin, seemed to us a more fimple and evident property, from whence to account for its strengthening virtues. And as some former Physiologists have supposed, (which our Author pretty expressly accedes to, page 59,) a visceral fermentation excited by the concurrence of the pancreatic juice and the bile in the Duodenum ; the Bark's fermenting to little together with the former (supposed fo fimilar to the laliva) and the bile, and very little, if at all, with the saliva alone, rather suggested to us, that one drachm of powdered Bark, did not wholly prevent the effervescence of half an ounce of saliva and as much bile, than that it was considerably, if at all, active in exciting their fermentation. Nevertheless, we shall not omit, that our ingenious and assiduous Experimenter obferves here, that a further probability of the fermentation of this valuable drug will ap pear in another place. That it contains air, which may be rendered elastic, without which there is no effervescence, is highly probable.

The fourteenth, a moft ufeful experiment, was made to di cover, whether wheat, barley, oats, or rice, were the foonest fermented, and, consequently, the most readily digestible. The event was, that the rice and barley mixtures (all four being huiked, well boiled, so as to burst the grain, and beat up with water and Aesh) were in brisk motion after an hour's warmth ; the mixture with the oats not till after four hours warmth ; and that with the wheat, was still three or four hours later. But when he hence infers wheat to be the most indigestible, he jus diciously adds, page 58 - But at the same time we see, that this property in wheat, renders it by much the fittest of all the Farinacea for the making of bread; as it appears to have firmnets fufficient to enable it to bear fome degree of fermentation in the baking, and yet vetain enough of its substance to undergo the alimentary furmentation afterwards in the body.'

'The fifreenth experiinent confifted in exciting an efferve· feence, by pouring an ounce of lemon juice on a drachm of falt "of wormwood in a cylindrical glass; and then confining, in the imprisoned air generated by the effervescence, a live sparrow, which expired in less tban half a minutes the same death haymy occuirèd, within the fame short period, to another, put by

Dr.

[ocr errors]

Dr. Hales, into the air. he had generated from heart of oak. Mr. Macbride here again expatiates on the good effects this air may nevertheless produce in the ftomach and intestines, however deadly in the lungs; and instances the very frequent and safe practice of giving Patients the aforesaid mixture of Riverius, in the very act of ebullition, which abundantly demonstrates it. And our Author's arguments and authorities here, for the blood's being fupplied with air through the chyliferous passages, rather than from the lungs, as some other Physiologists have supposed, collaterally fupport the same opinion.

The sixteenth experiment was contrived to discover, whether the fixed air would pass from a putrefying animal substance, into a caustic volatile alkali, such as fpirit of salt ammoniac with quick-lime, so as to render this caustic alkali mild and effervefcent. For the introduction of air into this liquid, of which it was before deprived by the quick-lime, proves such an analogous diluter of it, as water does of an inflammable vinous spirit, The event of the trial was, that the spirit of salt ammoniac with quick-lime, after imbibing the air emitted from putrid Aesh, effervesced with an acid, which before its resorption of air it could not.

The four subsequent experiments, to the twentieth inclusive, were made to discover, whether bodies become putrid from the access of air, as supposed to communicate some cause of putridity to them; or whether they become putrid, in consequence of the loss of some principle they before contained. The event was, that in repeated trials with different bits of beef and mutton, the morfels having been put in vacuo, under a cup with the bottom inverted on wet leather, and the air pumped out of it, in the open air, and in a cup which was filled up with melted suet-that the meat in the exhausted receiver, that under the cup, and that in the open air, tho' confiderably dried, became putrid in sixty hours; while that inclofed within the melted suet was perfe&tly sweet. A fresh egg confined in the receiver for a week, had then contracted a fetid or putrid smell ; at which time it was broke, and next morning was quite putrid and offensive; nor was its yolk near so firm as that of another egg of the fame laying, which had been exposed to the open air, and continued perfectly sweet. But in the twenty-first experiment, Mr. Macbride having inclosed, in a more compleat vacuum than he had procured before, one morsel of sweet fresh mutton, and put another of the same bulk under a glass, at the end of forty-eight hours he found that inclosed within the perfect vacuum sweet, and the other putrid. Hence he supposes the assertion of bodies not becoming readily putrid, when perfe&ly exeluded from the external air, may be true; notwithstanding the event of the

U 3

four

four preceding experiments; since he had not been able to effect lo compleat a vacuum in the glass receiver, as in the hollow metallic hemispheres. Yet he reasonably infers these former experiments incontestibly to prove, that removing the pressure of the atmosphere to a certain degree, does facilitate the escape of the fixed air (his cementing principle) from bodies.

The twenty-second experiment to the twenty-fifth inclusive, were repetitions of some of Dr. Pringle's, with respect to septic and antiseptic substances; and Mr. Macbride's ingenious and rational deductions from them, strongly coincide with the theory of his aërial cement, and are very obviously applicable to the subject of his fourth Essay, the Scurvy.

The remaining experiments in this Eslay, from the twen, ty-sixth to the thirty-fourth, were intended to investigate, whether putrid animal substances ought to be regarded as alkaline. The experiment number twenty-fix, answered in the affirmative, with respect to the putrid blood and serum together, after keeping them two months; and N° 27, with regard to the spirit distilled from it. The event of No 28, was in the negative, with respect to the putrid bile of an ox. By N° 30, the putrid human bile raised no ebullition with strong spirit of vitriol; but the distilled spirit of it, gave the alcaline greenness to sytup of violets; precipitated a solution of sublimate; and

heightened the blue colour of paper tinged with radith scrapings; r. yet, notwithstanding these strong tokens of an alkaline nature,

it effervesced but very obscurely on the affufion of strong fpirit of vitriol. It may be queried here, whether the different diet of the man, and of the quadruped, conduced to the confiderable difference of the operation of the spirit of the putrid human and brutal bile! The four last experiments are pretty similar to these; and the whole induce our assiduous Investigator to join with Neuman in saying, that as soon as an animal substance begins to putrefy, it also begins to discover an alkaline quality : and that the volatile matter now produced in it, may be separated by distillation, in a very gentle warınth. We may be certain our Author was particularly accurate in conducting these experiments, the effect of which has obliged him to diffent, though very philosophically, and politely, with Dr. Pringle and Dr. Lewis, with regard to the alcalescence of putrid Aleshy subftances : fome Gentlemen of knowlege in chemistry being prefent at his distillation of such substances, all of whom seemed satisfied, that these two eminent Physicians have been milled in this matter; and probably from inferring, that since alkalies bad been found by experiment to resist putrefaction, putrid animal substances must be very little, if at all, alkaline. But on this occasion Our Author very judiciously distinguishes, that the

principle

principle on which this action of alkaline salts depends, has nothing to do in particular with alkali, that being common to all saline bodies whatever, as falts.

The Essay on the respective Powers, &c. of the different Antiseprics, is not less curious than the former, and affords many fill more practical suggestions. It contains one short table of the effects of five different acids tried as antiseptics, by fresh mutton remaining in them from one to four days. A fécond brief table exhibits the different antiseptic powers of spirits of vitriol, of hartshorn, of a lixivium of tartar, and of a neutral mixture; fimple water being the common standard in all these experiments. A third table shews the force of four acids, that of the tartar being omitted, as correctors of putrefaction; the flesh immersed in them, on this occasion, being first rendered soft and putrid, by its standing four days in water moderately hot. A fourth table gives the effects of six different fermented liquors, tried as sweeteners of putrid Aesh. The experiments in this Elay are twenty-five, which concur very coherently with the ingenious arguments deduced from them, in establishing the Author's general proposition. But as the account of this curious and important treatise has insensibly, and, yet we think, unavoidably swelled upon us, we are obliged to retrench inuch of what appears both striking and entertaining to us, in this Effay, to join our Author in the following very pertinent and material query, with the answer to and reflection on it, as they occur, page 149.

< But here it may be demanded, what can these experiments prove, with regard to the restoration of putrid Auids, in a lima ing body? Is it possible to saturate these humours with fuch a quantity of air, as will be sufficient to correct their harpness, reKore their consistence, and bring back their sweetness ?

To this it may with safety be replied, that it is not only porfible, but that it is, perhaps, the only way by which this change can be produced.

• For we have seen, that there is a deception in regard to both acids and alkalies, when we suppose them to restore sweetness to a putrid animal substance ; that the first, so far from giving soundness to such kind of subftances, do in reality de Aroy their texture; and that the second only change the nature, but do not restore the original sweetness.'

· What he says, page 151, is another very interesting query, relating to the same topic; where, after admitting the certain power of alkalies to resist and correct putrefaction in dead bodies, he very rationally adds But whether, upon the presumption of

this

[ocr errors]
[ocr errors]
« VorigeDoorgaan »