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falve mell-fHh of a globofe elated form, furrowed in deep lines, and in fome fpecies imbricated, in others prickly, never auriculated, and always exprefling what we call the figure of a Heart. Hift. Nat. Eclairc. p. 332.
There are feveral very remarkable fpecies of this genus. The imbricated cordiform, or Heart-jhell, is a very elegant one ; the French authors call this the faitage, or roof-fhell, from its refembling the rafters on the top of a houfe. It reprefents in one view a Heart opened, but its great character is the ex- ternal work, which perfectly refembles the beams and rafters on the top of a houfe. The French call another fpecies of this the choux, or cabbage-fhell, from its being undulated like the leaves of fome of the garden curl'd cabbages. The Noah's-ark flicll is alfo of this genus, which no author has been able before to reduce to any genus at all. The name cordlformh is as old as Matthiolus's time, but never was made a generical term before.
The fpecies of the Cordiformes, or Heart -Jlulls , may be ar- ranged under feveral general heads : Some are of a very globular figure ; of thefe we have the following fpecies: 1. The yellow furrowed Hcart-JhelL 1. The grey fpinofe Heart-jhell. 3. The white furrowed Heart -Jhell. 4. The Cartijfa of Rumphius. 5. The thick Heart-jhell, with the cardo feparated from the apex. 6- The thick Heart-foell with the cardo at the apex. 7. The Corbula : This is an oblong Heart- jhell) very nearly approaching in fhape to the Jljell call- ed, the Noah's-ark jhell.
Some of the Cordtformes are of a triangular fhape ; of thefe we have the following fpecies : 1. The reticulated and fpottcd Heart-JlulL 2. The ftrawberry Hear t- jhell : This is ele- gantly variegated with (mail red fpots. 3. The white ftriated Heart-JJjell denticulated at the edge. 4. The variegated ftria- ted Heart- jhell, 5. The variegated and furrowed Hcart-jhell. 6. The ftriated gondola Hcart-jhell.
.Of thofe Cordljormes which are more nearly of the fhape of the human Heart, there are the following fpecies : r. The Heart-jhell variegated with rofe coloured fpots, and denticu fated at the edge. 2. The white circular Heart Jhell. 3. The fmall rofe-colour'd Heart-jhell.
4. Of the imbricated Cordljormes, we have thefollowing fpecies : 1. The Heart-jhell with great yellow lamina?. 2. The com- prefled Heart-jhell with yellow laminae. 3. The rofe- coloured Heart-jhell with yellow lamina?. 4. The oabbage-leafi&arr- jhell ; this is elegantly cut and curl'd in the manner of the leaves of fome of the curl'd. cabbages, and is beautifully variegated with fpots of red. 5. The common Noah's-ark /lull. 6. The yellow and white Noah's-ark Jhell, 7. The elegantly variegated Noah's-ark jhell. 8. The rare Heart-jhell defe'ribed by Fa- bius Columna : This is a foreign Jhell, and has its margin terminated in a point, and has an oblong hollow within. It is white and very tender. Hift. Nat. Eclairc, p. 330. HEAT [Cycl.y — The changes from Heat to cold are fometimes fo great and fudden in South Carolina, as to caufe 30 degrees difference in Fahrenheit's thermometer, in the fpace of a day. See Phil. Tranf. N° 470. Sect. 4. The Heat at Aftracan, in July 1746, was fo great as to raife Mr. de L'Ifle's thermometer, in the fhade, to the 89th de- gree, which correfponds to 103! of Fahrenheit's. And du- ring the whole month of July, and for feveral days in Au- guft, the thermometer was higher than what it rifes to by the natural Heat of the blood, which in Fahrenheit's is placed at 96. Mem. de 1'Acad. de Berlin, 1746. Hence it appears, that the opinion fome entertain of animals not being able to live in air heated beyond the heat of the hu- man blood, or the gb™ degree, is erroneous. All bodies heated beyond a certain degree, and applied to our bodies, give us pain, ifimulate, and inflame; when greatly heated they mortify whatever part they touch. Animal Heat. To what organs or operations the Heat of the human and other animal bodies is owing, is hitherto extreme- ly doubtful. The opinions which at prefent prevail, are, 1. That the Heat of animal bodies is owing to the attrition be- twixt the arteries and the blood. 2. That the lungs are the fountain of this Heat. 3. That the attrition of the parts of the follds on one another produce it. 4. That it is owing to the whole procefs, by which our aliment and juices are con- ftantly undergoing fome alteration.
The arguments in favour of the firft opinion are : That if an artery is tied or cut, the part to which it goes turns cold ; on the ceafing of the pulfation of the arteries, cold and death fol- low. An increafe of Heat attends a brilk circulation, and a languid circulation is accompanied with a fmall Heat. One who burns in a fever, or is hot with exercife, has a full and frequent pulfe ; in cold faintings, chlorous, &-c. the pulfe is fmall and flow ; and laftly, that the thermometer fbews the arterial blood to be a little hotter than that of the veins. This is accounted for from the conical figure of the arteries, from their flexures and branchings into exquifitely fmall capil- laries ; whence the refiffance and confequent attrition muft be great j from the number, firength, and claflicity of their coats; from the propelling power of the heart, and their ilfong refinance. From all thefe the particles of the blood perpetually getting new motions, directions, and rotations, arc attenuated, condenfed, have their angles ground off, and
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are made homogeneous : Hence the fluidity, ' red colour, and Heat of the mafs which is here perfected. But this theory is doubtful ; for what is faid of arteries, may be faid of any other parts, whofe functions are necefiary to life. The Heat and pulfation of the arteries do not keep together in anv regular proportion ; in fome morbid cafes there is a great feniible Heat, and a fmall pulfe ; and in others a full pulfe, and great coldnefs. Bcfides, all the length this demonfrration goes, is to fhew, that the motion of the arteries and Heat are gene- rally in proportion, which however does not fliew which is the caufe, and which the effect: ; nor indeed that either is the caufe or effect of the other, fince both may be the effects of fome other caufe. As to the proof by the thermometer, it fcems doubtful ; and what adds to the doubt is, that the ve- nal blood does not coagulate fo foon as the arterial. In fhorr, this theory is not eftabliihed by any fatisfactory and convin- cing proof.
The fecond opinion is, that the lungs .are the fountain of Heat in the human body. All that has been faid for the blood's being heated in the arteries, is advanced to prove this, hypothefis, with confiderable addition, viz. that in the Juries the blood vehels every where attend, divide, and fubdivide along with the ramifications of the wind-pipe; and as thefe are perpetually changing their fituation and form, becomino- longer or dorter, making more acute or more obtufc aiHes* fo rauft the concomitant blood-vefTels every moment make new angles, and give the blood new directions ; that at laffc the blood enters into an exquifitely fine net-work, foread every where on the vaftly thin air veficles, where thefe air- bladders are perpetually changing their angles, paints of con- tact:, their form, volume, interlaces, and fo forth. From thefe, and the elasticity of the air, and weight of the atmo- fphere, the blood is faid to be churned, prefled backward and forward, broken and kneaded together, diflblved and con- denfed, made red and hot in refpiration. This theory, how- ever plaufible, is not fatisfadtory For, 1. What was' faid be- fore of the improbability of Heat being generated by the fole attrition of fluids, takes place here. 2. Tho' the Iun^s be re- gularly fupplied with plenty of air, which has weight and elafticity enough to carry on the alternate fwelling and fubfi- ding of the veficles ; yet life and Heat foon fail, if that air has, by palling through the fire, or any other way, been robbed of fome particles or quality, different from its weight and elafticity. 3. The argument from the additional action of the folids of the lungs on the blood, more than what is found in the arteries, from their greater and conftantly varying mo- tion, fcems to be fully taken off by one part of Flock's ex- periment, exhibited before the royal focicty, in which the lungs of a dog being kept conftantly diftended by a frefh blah: of air, the dog lived, and his heart beat regularly : So that there is no need for that frequent and great variation of an- gles, and- points of contact:, upon which the additional attri- tion is built. 4. That the cold air rufhing into the fponsy lungs, on the numberlefs air-bladders, on which the blood^is aimoft fuperficially fpread, fhould make the blood hot, is an improbable opinion, and fupported by no proof. And as the caufe appears not at all promifing a priori, fo the effect feems to demonftrate this not to be the caufe. For, 5. That the blood is rather cooled than heated in the lungs, may be infer- red from the benefit received by the ihfpiration of cool air in many inflammatory difeafes, efpedally thofe of the lungs. In burning fevers, with a full quick pulfe, red fkin, and a large and quick refpiration, relief has often been given by opening a window, and admitting a ftream of cool air to breath in : The effects of which has been obferved to be, that tho' the body was clofe covered, yet in one minute the refpiration be- came flower, and very foon after the pulfe abated of its full- nefs ; and not only the face, but the whole body, of its fiery Heat and colour. 6. If the blood Was heated in the lungs, we fhould need lefs of their function, when we are warm, or in a warm place, the Heat of our bodies, or of the atmo- fphere, doing fo much of the office of the lungs ; and that we mould want more of it, when cool, or in cool air. But when we are hot, and want to be cooled, we breathe full and quick ; and when we are cold, and want to be warmed, our refpira- tion is flow and fmall j contrary to what one would expect-, if the action of the air on the blood in the lungs were to heat it. 7. The blood which comes from the fmall veffels of the lungs, is not more expanded than before, as has been afferted, but not proved by any experiment, which it would certainly be if it was hotter; for liquors rarify by Heat, and few more than blood. 8. If the blood owes its Heat to the action of the lungs, we muft look out for another fource of Heat in the egg and foetus. To the objection, that the Heat of the mo- ther is fufficient for the purpofe, till this new function comes into action, two obfervations may be oppofed : The firft is, that toward the end of incubation, an egg may be left by the dam, in a cold feafon, for a little longer time than would be fafe for the chick, if all its Heat depended upon her ; yea long enough for an egg, that contains no warm principle to become of the temperature of the ambient air ; yet upon opening it, the chick has been found neither quite fo cold, nor dead. The fecond is, that a ripe fcetus, taken away from the mother, but continuing within the membranes, can live
feveral
