An Efay on the Theory of the Production of Animal Heat, and on its Application in the Treatment of Cutaneous Eruptions, Inflammations, and fome other Difeafes. By Edward Rigby. 8vo. 45. ferved. Johnson.

WE

E always attend on Mr. Rigby with pleasure; for we feldom feparate from him without inftruction. Even his mistakes are falutary leffons, and teach us to reprefs too great confidence in our own efforts. The work before us confifts of two parts, which are more diftinct than the author probably intended them to be; and if he fails in the one, yet as the other is not founded on, but rather loosely connected with it, the ruin will not be either general or fatal. The theory of animal heat has engaged the attention of many eminent philofophers; and, though each fees the oblivion into which his predeceffors have fallen, the temptation is too strong to be refifted; the delufion too pleafing to be conquered. Like the fancied heroine of the Arabian Nights' Entertainments, though the daily brides had, each fucceffive morning, been led to the fcaffold, the honour of the conteft, and the glimmering hopes of fuccefs, concurred to make her eager for the fupreme dignity. Our readers will suppose, that our review of fo many literary fpectres haftening to condemnation, would give us no very favourable difpofition towards Mr. Rigby's work, notwithstanding our avowed partiality for the author. Yet, as ufual, we endeavoured to examine with caution, and determine with candour: as fo many had wandered, one might now be right; and former errors might have contributed to direct a fucceffor.

The last theory which had the fmalleft claim to the attention of the learned, was that of Mr. Crawford, which we reviewed in our forty-eighth Volume, page 181. The merit of the opinion refted on the evidence of the facts, and it cannot be expected that Reviewers should delay their accounts of experimental enquiries till they have afcertained the truth of the experiments. We applauded the author's induftry, and waited for the refult of other examinations. The principal work, in this line, was one by Mr. Morgan *, who, with great acutehefs and precifion, examined every part of the author's reafoning, and his feparate facts. There was much reafon to fuppofe, that Mr. Crawford had obferved and reafoned with too great hafte: perhaps the author may have thought the fame; for we have yet heard no reply, nor has the theory been e-published. We have given this little sketch chiefly to ob * See Crit. Rev. vol. li. p. 212:

VOL. LX. Aug. 1785.

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Serve, that the principle on which Mr. Crawford began is pro bably well founded his errors were undoubtedly numerous, and ought to have been again examined. If the diftinction between abfolute or latent, and fenfible heat, be established, it will then be only neceffary to enquire, whether the change which the blood undergoes in the courfe of circulation, can make any alteration in its capacity to retain heat. If this be true, and the change is fuch as to leffen the quantity of abfolute heat, which there is great reason to believe, the foundation is clear. The fuperftru&ture may be just or erroneous; it may be rejected or retained; for enough will be established. But it is time to proceed to the work before us.

Mr. Rigby fuppofes that heat is a body, and therefore capable of entering, as an ingredient, into the compofition of other bodies. The fubftances which are conveyed into the ftomach abound with this ingredient; and he justly obferves, that when its feparation is the confequence of almost every decompofition with which we are acquainted, it is abfurd to fuppose, that heat should not efcape during the decompofition of the fubftances containing it, in the ftomach. Mr. Rigby em ploys his firft fection not only in proving his general conclu fions, but in fhewing how nature has attended to them in a variety of instances, and in what degree fatiety and hunger, leanness and obesity, are connected with abundance or fearcity, with the more or lefs rapid efcape of the heat which enters into the human fyftem.

The great defect of every fyftem on the subject of animal heat has been the want of obfervations, or rather of experiments, on the bodies of animals. The first circumstance, which feems to weaken the opinion of Mr. Rigby, is his fuppofing that there is one particular fource of heat. If this were true, the ftomach fhould be the warmest part, and the heat fhould gradually decrease till we arrive at the extremities. But, in the few experiments made on this fubject, we find that this is not decidedly true. The mouth, the axilla, and the groin, raife the thermometer to the fame height. The urine has no greater effect on it than a fiftulous ulcer in the thigh; and, in a rabbit, the thermometer, placed between the muscles of the leg, was at the fame point with one inferted into the abdomen. These facts certainly fupport that opinion, which attributes the heat to a power acting at the fame time in every part of the fyftem; and there are now two opinions of this kind, which deferve our attention; the one, that it proceeds from the energy of the nervous power; the other, which attributes it to the chemical change conftantly going on in our fluids. If Mr. Rigby's opinion were true, it should be the best me

thod of leffening the heat, to evacuate the contents of the ftomach and bowels; but this effect of laxatives and emetics is very inferior to that of bleeding, even in fmall quantities, which increases the power of the digeftive organs. The heat is indeed increased after a full meal; but it is not felt in the ftomach thofe, whofe heat is particularly increafed by digeftion, feel it rather in the palms of the hands, and foles of the feet. Indeed every circumitance feems to fhow, that the heat is rather the confequence of a general change in the fyftem, and attended with all the fymptoms which accompany it, when excited by a more external caufe. Again: the heat of the body is alnoft conftantly the fame in all ages and fexes, though the diet is materially different; and the diet, if it be alimentary on the one hand, and excefs be avoided on the other, is found to make little variation. These extremes would alter the fubject by inducing difeafe, and we are now speaking of health. We need not, at this period, enlarge on the great difference in the chemical properties of fubftances really alimentary: the matter of heat has been fo lately the fubject of our experiments, that we cannot decide on its relation to our different foods; but, from its connection with phlogifton, we may fuppofe that its quantity must be very various, though its effects in producing heat are uniform. The fubject of difeafes would lead us too far; but we fhould find in fevers of different kinds, fome very ftriking objections to the opinions of our author.

We have freely given the chief arguments which have induced us to reject Mr. Rigby's opinion; but we are induced, by his particular defire, to confider the firft as one of the leaft important of his various fections: yet we ought to add, that it contains fome new and fome ingenious remarks. The uti lity of them is in a great degree diminished, by the author's adopting an error of Dr. Priestley, that the nutritious principle is phlogiston; for he ought to have obferved only, that the moft nutritious fubftances are phlogiftic. In fact, phlogiston is fo far from being the nutritious principle, that it more commolny and abundantly appears among the excrements. The bile is an highly animalifed and phlogiftic fluid; but its great ufe is rather to prepare the crude aliment for absorption, than to nourish: it is again rejected, perhaps ftill more highly phlogifticated. Mr. Rigby, however, foon proceeds to the appli cation of his doctrine.

Whether the philofophical reader will admit the preceding theory of the production of animal heat to be probable or not, the foregoing facts are certainly fufficient to prove, that a confiderable quantity of heat is conftantly generated in the animal body, and that fome of it has a conftant tendency to pass off

by the furface; that the regular escape of this matter depende upon fuch various circumstances, that it must be liable to occafional interruptions, and that in confequence of thefe interrup-tions, the furface of the fkin must be fometimes overcharged with heat.

The effect of this accumulation of heat from within, if we may be allowed to confider the fact fimply, must be precifely. the fame as if an extraordinary quantity of heat were to be applied to the fkin from without; and which is well known to be as follows: a fmall degree of heat, and which is not long continued, excites only an increased fenfibility in the part; if a larger quantity, or if longer continued, it occafions a fenfe of burning, the part becomes red, is inflamed, and tumefied, perhaps, by the fimple expanfive power of heat; and if still more be applied, the circulation in the cutis is obftructed, and a decompofition takes place, which is attended either with the vefication or exulceration of the part.

In this inftance, which we may confider as a specimen of our author's reasoning, we fufpect a confiderable mistake; itis very doubtful whether the heat produced on the furface is a primary or a fecondary effect; or more ftrictly, whether it is a mere evacuation of a fuperabundant principle, or the confequence of a very different evacuation. We fufpect it to bet fecondary, because we can excite it by raifing inflammation, without primarily increasing the heat of the fyftem; by the milky juice, for inftance, of some very acrid plants applied in a quantity, which fo far from confining the heat of the part, contributes to leffen it by evaporation. We can leffen it by causes which, according to the author's fyftem, ought to increase it; because they do confine the heat, viz. by the application of dry powders in eryfipelas, by using flannel linings to breeches worn in riding. The one prevents the spreading, by really abforbing the caufe of the eruption, viz. the acrid ferum; the other prevents excoriation, by abforbing the perfpirable matter. In most of the eruptions, from attrition, the inflammation feems to be firft excited; and Mr. Rigby knows that the fecretion from inflamed glands is always viated, and very generally rendered highly acrid. There is one fact. which, on this fyftem, we are unable to explain, viz. the eruptions which arife on applying a cold cabbage leaf behinda child's ear.

But though Mr. Rigby feems, in our opinion, to have erred: in the explanation of fome phænomena, yet, in the more effential refpects, his work is highly valuable and important. By diminishing the heat of the part, if the fuperabundant: heat be really the cause of the eruption, we directly removeit; if it be only a concomitant fymptom, all our powers em

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ployed in leffening heat are also fedatives, and oppose inflammation. It is a pleafing reflection, therefore, that we can ultimately agree; and we think his condemnation of poultices, ointments, and other bad conductors of heat, perfectly just; for coolers are not only fedatives, but to prevent the diffipation of heat, if we do not by the fame means obviate its other effects, increases the inflammation.

Yet, in fome of the cutaneous eruptions of children, which have been preceded by fickness, head-ach, &c. coolers are certainly precarious remedies; and we wish that our intelligent author had added fome cautions refpecting them. With regard to the fmall-pox, and miliary fevers, we fully agree with him. Free cold air, in the meazles, is of more doubtful authority, and our author feems to hefitate in recommending it; but we fully agree with him in the propriety of using a tepid bath, the heat of which is fomewhat below the heat of the fkin we fuppofe about ninety-two or ninety-four degrees of Fabrenheit.

In

In erysipelas and fcarlatina, we believe cold to be highly ufeful; but when either difeafe is violent, and attended with putrid fever, we should fufpect the propriety of cold applications in any very great extent, left we bring on gangrene. fmaller degrees, cold will be one of the most powerful means of preventing it; and we prefume it will be always neceffary to ufe free cold air.

In the elephantiafis, the application of cold is probably more doubtful, because it is never attended with any very great heat, and its caufe feems to lie beyond the power of external medicine. Of its ufe in the fcald-head, we think more favourably, and shall infert a cafe in which it fucceeded completely. After defcribing the difeafe, Mr. Rigby observes,

The fubject of heat, at this time, particularly engaging my attention, it occurred to me, that this complaint might, poffibly, be in fome meafure produced by an accumulation of it; at leaft, whatever was the cause of it, it appeared very probable that the large and increafing fcab which covered the dif eafed furface, retarded the cure, on the principle of its preventing the natural efcape of heat, it being, evidently, of fuch a loose texture, as to be a very flow conductor of it. I refolved, therefore, immediately to try whether keeping the part conftantly moist with wet rags would not relieve it, by favouring the efcape of heat from it; but as whilst the thick cruft was interpofed between the furface of the head and the wet rag, its influence could but be felt in a very fmall degree; I previously removed the fcab, by an ointment flightly impregnated with a decoction of cantharides, it being compofed of the unguentum epifpafticum of the Edinburgh difpenfatory, and two.

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