Befides the general fuppofition of an independent living principle, an inference has been drawn, from the facts we have noticed, of a nervous energy, independent of the brain. It may therefore be proper to explain the fenfe in which the uncertain term of nervous energy is employed in this effay, left it should be confounded with the notion of a vital principle. By this term then, I mean that condition, derived from the brain, to different parts of the body, by means of which they become capable of motion. In this definition I allude to no theory refpecting the nature of the foul, nor refpecting the fpecific nature of the nervous energy, but confine the terms to facts. The proof of the definition will appear, from the arguments I am going to mention. To fhew, by direct proof, that there is no independent vital principle, I would observe, 1. That it is juftly urged by Dr. Monro* against the doctrine of the vis infita, that there is too much defign in the actions of different muscles, affected by different ftimuli, to be the effect of mere mechanifm. This argument is ftrongly against the existence of a vital principle. Thus, when the hand or foot is burnt, or otherwife fuddenly injured, the mufcles on the part immediately ftimulated are not thrown into • Obfervations on the Nerv. Syft. p. 95 to 99. action, action, nor the muscles on the fide irritated; but their antagonists contract immediately and ftrongly if the back of the hand, for inftance, be fuddenly irritated, the extenfors of the hand are not affected, but the flexors are thrown into instant and violent action, to remove the limb from the offending caufe. Now if the inftantaneous action be, in this cafe, chiefly produced by an effort of the mind, the fuppofition of a distinct vital principle is fuperfluous; if it be faid to be produced by the living power indedendent of the mind, then there must be a rational power in the body, independent of the mind, which is abfurd. 2. The ftate of the vital and involuntary motions is confiderably affected by the ftate of the mind. Refpiration is, to a certain degree, under the direction of the will: the action of the heart is very quickly and powerfully varied by the workings of the paffions; and even the fecretions are frequently changed, in quantity and quality †, by the fame cause. But farther, these motions are often fufpended by a sudden affection of the mind, as in the cafe of fainting, which is produced very commonly by an impreflion made on the mind, without the fufpi * Whytt, Vit. and Inv. Mot. + The bite of an enraged man has been known to prove fatal, in confequence of the poifonous quality of the faliva. HOFFMAN, tom. I, cion of any bodily caufe; and the impreffion is sometimes fo powerful as to put an entire ftop to the vital motions, and thus produce death. Again, organic lefions of the heart and lungs have been obferved to take place from extremes of paffion; and particularly, in Mesmer's operations of animal magnetism, several persons spit blood by the mere strength of imagination. All these facts equally disprove the existence of a feparate vital principle, and prove the dependance of the nervous energy upon the brain. 3. It is acknowledged, that in maniacal cafes, the principal part of the disease confifts in depraved perception; and this depravation implies a change in the medium of perception, that is, in the brain and nervous fyftem. Now it is well known that madness is frequently produced by causes purely mental, and in perfons apparently in good health. And as the patient's sensibility to very powerful ftimuli is much diminished in maniacal cafes, they afford another proof of the fubordination of the nervous energy. 4. Writers of unquestionable credit have obferved, that, in paralytic cafes, motion is frequently destroyed, while fenfe remains t; as • See the Report of the Commiffioners. + Haller. Phyf. tom. IV. p. 390. the the cause of palfy almost always refides in the brain, this fact appears equally inexplicable, on the opinion of a diftinct living principle, or of a nervous energy independent of the brain. 5. When nerves are regenerated, after being cut through, fenfation and voluntary motion are not always reftored to the parts beneath the divifion the restoration was never made in Dr. Monro's experiments*. But on the fuppofition of a diftinct nervous power, the nerve, after its re-union, ought to refume all its offices. 6. Dr. Whytt afferts, that when the spinal marrow of a frog is destroyed, after decollation, no contraction can be excited in the limbs by cutting or tearing the muscles†. While fo many doubts occur respecting the proof of a vital principle, and while the fuppofition includes fo many difficulties, in its own nature, it is allowable to fufpend our judgment on the fubject, till more convincing proofs of its existence fhall appear, than have as yet been offered to the public. At prefent, it is evident that we gain nothing by admitting the fuppofition, as no distinct · account is given of the nature or production of this principle, and as an investigation of facts feems to lead us back to the brain, as the fource of fenfibility and irritability. • Obfervations, p. 27. + Obf. on Irritab, and Senfib. p. 284. In the course of this paper, I have uniformly confidered the action of the mind and brain on the body as identical, without reference to the question of materialism, because with refpe&t to our facts, and indeed to all medical facts, this notion is fufficiently complete. I have also avoided all difquifitions refpecting the peculiar nature of the nervous energy, convinced, that in the present ftate of our knowledge it is of more confequence to examine one opinion, which is faid to be fupported by facts, than either to reject or advance many plaufible hypotheses. I have purposely omitted to confider the application of the doctrine of a vital principle to pathology, as the fubject would lead to difquifitions inadmiffible by the rules of the Society. On the COMPARATIVE EXCELLENCE of the SCIENCES and ARTS; by Mr. WILLIAM ROSCOE. Communicated by Mr. M. NICHOLSON. I in READ MARCH 28, 1787. HERE is perhaps no circumstance more injurious both to our improvement and happiness, than a propenfity to engage, and perfevere, in the study of particular branches of VOL. III. R. fcience, |