Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/51

 JE T H (33 « flows copioufly into the medullary part of the nerves, “ when no obttacle Hands in its way : but, when once “ it has got there, it keeps firm poffeflion, and never “ afterwards leaves it. Now,” fays he, “ a quan“ tity of aether probably conftitutes one of the flamix“ nal parts of animal bodies, and increafes in propor‘ tion to their age and growth: For nothing is more “ ridiculous than to fuppofe that what is .commonly “ called the nervous fluid can be daily wafted by-la“ hour a.nd exercife, and daily repaired by a new fe“ cretion from the brain. To refute this vulgar no“ tion, nothing more is neceflary than to fay. That “ it is one of Boerbaave's theories, and mujl be falfe, “ as all Boerhaave’s other theories have been proved “ to be ill-founded ! But aethgr is of a more fixed f“ and determinate nature ;t whenever it gets pofleflion ‘ of any fubftance, it never forfakes it, unlefs the “ texture and conftitution of the body itfelf be chan“ce ged. Hence,” continues our author, “ the tether of an acid body remains as long as the body conti‘£ nues to be acid; the fame obfervation holds with “ regard to the aether of an alkaline body: But, if “ thefe two be blended together into a neutral fait, <£“ the tether muft .likewife be changed into a neutral; and therefore, in the formation of the medullary “ or ftaminal part of animals, the aether v/hich before “ belonged to, or had the properties of fome other fub“ ftance, is inftantaneoufly changed into animal Kther, “ and remains fo till the diflblution of that animal.” Our author next obferves, “ That bodies require to “ be in a certain ftate or condition in order to the for“ mation of an aether that is proper for them. This “ condition of bodies is called an excitedfate: Thus, “ as fulphur, when fluid, does not receive the eleftric “ matter, but, when folid, inftantly receives it; in “ the fame manner, the nerves, though properly “ formed, do not admit an aether adapted to their “ nature, unlefs they be in an excited ftate. Hence,” fays he, “ the xther of a dead, and that of a living “ perfon, are very different, although the texture and “ figure of the nerves be the fame. The ftate necef£!“ fary for conftituting the xther of a living animal, feems to depend on heat and moifture; becaufe thefe “ things are abfolutely neceflary in the conftitution of “ life: And hence,” concludes our author, “ the ex“ cited ftate of the- nerves depends on heat and moi“ fture. There are alfo certain circumftances,” fays he, “ which contribute to render the ftate of the “ nerves more or lefs apt for accumulating xther: A fpafmodic fever, for example, renders the nerves of “ the whole body .lefs pervious to the motion of the “ xther ; and hence, in cafes of this nature, health, “ ££and all the vitalfundions, muft be injured.” Thefe,” our author obferves, “ are the outlines “ of a neon dodtrine concerning the nature and func“ tions of the nerves;” and, upon this foundation, proceeds to give his new theory of animal heat. ££ From the foregoing reafoning," fays he, “ the “ heat, as well as all the fundtions of animals, feem “ to be occafioned by the ofcillations of the nervous “ xther betwixt the extremities of the fentient nerves Vol. I. No. 2. 3

) iE T H “ and the brain, or, more properly, betwixt the brain “ and mufcles. But eledtrical xther, as above ob“ fcrved, varies a little from common xther; all in“ elaftic fluids, as was.likewife formerly remarked, “ are non-eledtrics ; and all fclid bodies, metals ex“ cepted, are eledtrics: Thefe circumftances,” fays our ££ author, “ feem to he owing to the ofcillations of the eledtric matter in bodies. In the fame manner,” fays he, “ the nature of animals may be fuch, and the “ nerves may be fo conftituted, as to form an xther ad“ apted to their nature, and to excite thofe ofcillations “ which occafion animal heat. The wonderful effedls “ of heat(f and cold upon the nerves,” continues our author, confirms this theory: Every adtion, and “ even life itfelf, requires a certain degree of heat; “ for, as the heat of the external air is fo variable, it “£ was abfolutely necefiary that animal bodies Ihould ££ of heat fuited to their nature, independent of external circumftances : Hence we fee the reafon why “ the degree of heat fo feldom varies in the fame fpe“ eies of animals. However, although the nervous “ xther is always ready for exciting heat by its ofcil“ lations ; yet, in order to bring about this effedt fuc“ cefsfully, external Jlimuli ate neceflary, otherwife “ the xther would be in danger ofJlagnating, which C£“ would occafion fleep, a palfy, and, laft of all, death. The moft permanent of thefe ftimuli is the-pulfa“ tion of the arteries; which is the reafon why heat “ is fo connedted with the circulation of the blood, “ and why many authors have miftaken it for the true “ caufe of animal heat.” Our author now concludes with obferving, “ That “ by his theory, the varieties of heat in different parts “ of the body, the heat and fluffing of the face from “ ftiame, and all the other phxnomena of heat in ani“ mal bodies, admit of abetter explanation, than by “ any other theory hitherto invented.” Having thus given a pretty full account of an attempt to explain the moft abftrufe operations of nature, as nearly as poflible in the very words of the author, we cannot deny ourfelves the liberty of making a few obfervations. To give a formal refutation of this author’s reafoning, is no part of our plan. It is, perhaps, wrong to fay that he has reafoned; for the whole hypothetical part of his eflay is a mere farrago of vague afiertions, non-entities, illogical conclufions, and extravagant fancies. His xther feems to be an exceedingly tradlable fort of fubftance: Whenever the qualities of one body differ from thofe of another, a different modification of ather at once folves the phxnomenon. The xther of iron muft not, to be fare, be exadtly the fame with the nervous xther, otherwife it would be in danger of producing fenfation in place of magnetifm. It would like wife have been very improper to give the vegetable xther exadlly the fame qualities with thofe of animal xther; for, in fuch a cafe, men-would ruii great rifle of ftriking root in the foil, and trees and hedges might eradicate "and run about the fields. Nothing can be more ludicrous than :o fo: I a
 * ££ be endowed with the faculty of producing a degree