ART. IV. Philofophical Tranfactions of the Royal Society of London, for 1809. Part I. Part I. 4to. 220 pages. Nicol.

1809.

WHEN we lamented the death of that excellent philofopher Cavallo, we felt for our own lofs as well as that of the public. On him we had long depended for philofophical opinions, and the delay of the prefent Report is one of the confequences of that lofs. We trust that it is now repaired, and that we shall proceed in future with equal accuracy and vigour.

1. The Croonian Lecture on the Functions of the Heart and Arteries. By Thomas Young, M. D. For. Sec. R. S.

"The mechanical motions which take place in an animal body," fays Dr. Young, " are regulated by the fame general laws as the motions of inanimate bodies. Thus the force of gra vitation acts precifely in the fame manner, and in the fame de gree, on living as on dead matter. It is obvious, therefore, that the inquiry in what manner and in what degree the circula tion of the blood depends on the mufcular and elaftic powers of the heart and arteries, fuppofing the nature of thofe powers to be known, must become fimply a queftion belonging to the most re fined department of hydraulics."

Agreeably to this view of the fubject, the author proceeds to inquire, 1. What would be the nature of the circulation of the blood if the whole of the veins and arteries were invariable in their dimensions, like tubes of glafs or bone? 2. In what manner the pulle would be tranfmited from the heart through the arteries if they were merely elastic tubes? 3. What actions we can with propriety attribute to the mufcular coats of the arteries them felves. Laftly, are added fome obfervations on the difturbances of thefe motions, which may be fuppofed to occur in different kinds of inflammatory fevers.

Confidering the blood veffels as tubes of invariable dimen、 fions, and the motion of the fluid as uniform, we are to fuppofe the blood in the arteries as fubjected to a certain preffure, by means of which it is forced into the veins; and this preffure originating from the contraction of the heart, and continued by the tenfion of the arteries, is almoft entirely employed in overcoming the friction of the veffels.

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BRIT. CRIT. VOL. XXXVIII. OCT. 1811.

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The magnitude of the preffure is inferred from Dr. Hale's experiments on quadrupeds, to be equivalent to a column of feven feet. The diameter of the aorta is affumed at of an inch, and is fuppofed to branch off thirty times fucceffively in ramifications of two trunks each time until the last veffels become only To part of an inch in diameter.

Taking thefe data for granted, the author then employs the theorems which he has given in a former paper for calcu lating the refiftance.

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He eftimates the quantity of blood contained in the arteries at 9 or 10 pounds, and fuppofes the heart to throw out at each pulfation 1 ounce of blood. The velocity of the blood in the aorta 9 inches, and in the fmalleft veffels an inch per fecond. The refiftance which the blood would meet in circulating through thefe veffels, which he fuppofes, on account of its vifcidity, to be four times as great as that of water, he calculates is equivalent to a column of 80 inches.

The effect of the curvature of the arteries in increafing the refiftance is next confidered, but is found to be fo exceedingly finall as not materially to affect the calculation.

The fucceffive tranfmiffion of the pulfations of the heart through the length of the arteries is confidered as analogous to the motion of the waves on the furface of water, or that of found tranfmitted through the air; the coats of the arteries are fuppofed to be perfectly claftic; hence it follows that the velocity of the pulfe muft in this cafe be nearly the fame as that tranfmitted through an elaftic fluid, under the preffure of a column of the fame height as that which meafures the actual arterial preffure; that is, equal to that which is acquired by a heavy body falling freely through half this height. In man this velocity is about 15 feet per fecond, to which the progreffive motion of the blood itfelf adds about 8 inches, fo that the velocity of a pulfation may be confi dered equal to about 16 feet per second.

The mean velocity of the blood in the aorta being inches per fecond, and the contraction of the heart occupying only of a pulfation, the greatcft velocity of the blood in the aorta mufl be 25 inches per fecond, or about part of the velocity of the pulfe; fo that a column of blood occupying inches may occupy only 7; hence the diameter of the vessel must incrcafe about part, the tenfion will become greater, and the force of the heart to fupport fuch preffure must be equivalent to a column of 101 inches, which agrees very well with an experiment of Hales on the

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afcent of the blood, in a tube connected with the artery of a horse.

The author then proceeds to inquire into the functions which are to be attributed to the mufcular fibres of the coats of the arteries, which he apprehends are much less concerned in the progreffive motion of the blood than is generally believed.

"There is no difficulty," fays Dr. Y., " in imagining what fervices the coats of the arteries may be capable of performing, without attributing to them any immediate concern in fupporting the circulation; for fince the quantity of blood in the fyftem is on many accounts perpetually varying, there must be fome means of accommodating the blood veffels to their contents."

Agreeably to this opinion, the author attributes the nature of the pulfe, as perceptible to the touch, almoft entirely to the action of the heart.

The deviations from the natural ftate of the circulation are next confidered, and are either general or partial. Ge. neral deviations confift in a change of the motion of the heart or of the capacity of the capillary arteries. When the quantity of the blood tranfmitted by the heart is fmaller than in health, the arteries must be contracted and the veins diftended. In this flate the pulfe muft be small and weak, which will occafion palenefs, and chilliness of the extremities until the blood accumulated in the veins urges the heart to greater activity, and occafions it to propel an unnatural quantity of blood; hence a contrary ftate may arife, the state which perhaps conflitutes the hot fit of fever.

Exceflive relaxation of the arteries may be the principal caule of another general derangement of the circulation; the motion of the blood will be accelerated, the arteries emptied, and the veins overcharged, and the heart be exhaufted by fruitlefs efforts to reftore the equilibrium. This ftate appears to refemble in many refpects the affections obferved in typhus.

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If we fuppofe fevers to be occafioned by derangements of the larger arteries, we may in like manner fuppofe local inflammations to be occafioned by excellive dilatation or contraction of the smaller veffels.

Befides thefe general illuftrations of the nature of fevers and inflammations, the author is of opinion that this theory may fometimes be of ufe in explaining the operation of the remedies employed for relieving them. It affords reason to fuppofe that venefection must be more rapidly and powerfully felt in a neighbouring than in a diflant part, and to

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expect more speedy and efficacious relief in inflammations from opening an artery than a vein. It also shows us why greater benefit is often experienced from withdraw. ing a small portion of blood by means of cupping or leeches than a much larger quantity by venefection.'

II. An Account of fome Experiments, performed with a View to afcertain the most advantageous Method of conftructing a Voltaic Apparatus for the Purposes of Chemical Refearch. By John George Children, Efq. F. R. S.

"The late interesting difcoveries of Mr. Davy having shown the high importance of a voltaic battery as an inftrument of che mical analyfis, it became a defirable object to afcertain that mode of conftructing it by which the greatest effect may be produced, with the leaft wafte of power and expence."

For this purpofe the author conftructed two voltaic batteries, and from the effect which they produced draws the following conclufions; that

"The abfolute effect of a voltaic apparatus, therefore, feems to be in the compound ratio of the number, and fize of the plates the intenfity of the electricity being as the former, the quantity given out as the latter; confequently regard must be had, in its conftruction, to the purposes for which it is defigned. For experiments on perfect conductors, very large plates are to be preferred, a small number of which will probably be fufi. cient; but where the refiftance of imperfect conductors is to he overcome, the combination must be great, but the fize of the plates may be fmall; but if quantity and intenfity be both required, then a large number of large plates will be neceffary. For general purpofes, four inches fquare will be found to be the

moft convenient fize.

"Of the two methods ufually employed, that of having the copper and zinc plates joined together only in one point, and moveable, is much better than the old plan of foldering them together, through the whole furface, and cementing them into she troughs: as, by the new construction, the apparatus can be more easily cleaned and repaired, and a double quantity of furface is obtained. For the partitions in the troughs, glafs feems the fubitance beft adapted to fecure a perfect infulation; but the best of all, will be troughs made entirely of Wedgewood's ware, an idea, I believe, firt fuggefted by Dr. Babington." P. 37.

. III. The Bakerian Lelure. An Account of fome new AnaIstical Refearches on the Nature of certain Bodies, particularly the Alkalies, Phojphorus, Sulphur, carbonaceous Matter, and the

Acids hitherto undecompounded; with fame general Observations' on Chemical Theory. By Humphrey Davy, Efq. Sec. R. S. F.R. S. Ed. and M. R. I. A.

1. Experiments on the Action of Potassium on Ammonia, and Obfervations on the Nature of thefe two Bodies. In thefe experiments the author at firft employed potaflium procured by electricity, but he foon fubftituted for it the metal obtained by the action of ignited iron upon potafh, in the method difcovered by M. M. Gay Lufac and Thenard, finding that it gave the fame refults, and could be obtained of an uniform quality in larger quantities, and with much lefs labour and expence.

A green glafs retort was exhaufted, filled with hydrogene, exhaufted a fecond time, and then filled with ammonia. In this way the gas was operated upon in a high degree of purity.

"When ammonia is brought into contact with about twice its weight of potaffium at common temperatures, the metal lofes its luftre and becomes white, there is a flight diminution in the volume of the gas; but no other effects are produced. The white crust examined proves to be potash, and the ammonia is found to contain a fmall quantity of hydrogene, usually not more than equal in volume to the metal. On heating the potaffium in the gas, by means of a fpirit lamp applied to the bottom of the retort, the colour of the cruft is feen to change from white to a bright azure, and this gradually paifes through fhades of bright blue and green into dark olive. The cruft and the metal then fufe together; there is a confiderable effervefcence, and the cruft paffing off to the fides, fuffers the brilliant furface of the potaf fium to appear. When the potaflium is cooled in this ftate it is again covered with the white cruft. By heating a second time, it fwells confiderably, becomes porus, and appears crystallized,' and of a beautiful azure tint; the fame feries of phenomena, as those before described, occur in a continuation of the process, and it is finally entirely converted into the dark olive coloured fubftance." P. 42.

This fubftance poffeffes the following properties;

1. It is cryftallized and prefents irregular facets, which are extremely dark, and in colour and luftre not unlike the prot. oxide of iron; it is opaque when examined in large maffes, but is femi-transparent in thin films, and appears of a bright brown colour by tranfmitted light.

"2. It is fufible at a heat a little above that of boiling water, and if heated much higher, emits globules of gas,

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3. It