2-1 INTRODUCTION. 



the aliment irritates [or excites] the intestine, the blood irritates the heart, &c. These 

 movements are all independent of the will, and in general (while health endures) take 

 place without the cognizance of the me ; the nerves which produce them ha\'e even, 

 in several parts, a different distribution from that of the nerves affected by sensations 

 or subject to the will, and the object of the dilFerence appears to be the securing of 

 this independence.* 



The nervous functions, that is to saj', sensitiveness and muscular irritability, are so 

 much the stronger at every point, in proportion as the exciting cause is more abundant; 

 and as this agent, or the ners'ous fluid, is produced by secretion [or evolution], its 

 abundance must be in proportion to the quantity of medullary or secretory matter, 

 and the amount of blood received by the latter. 



In animals that have a circulation, the blood is propelled through the arteries \'>liicli 

 convey it to its destined parts, by means of their irritability and that of the heart. If 

 these arteries be irritated, they act more vigorously, and propel a greater quantity of 

 blood ; the nervous fluid becomes more abundant, and augments the local sensibility ; 

 this, in its turn, increases the irritabdity of the arteries, so that this mutual action may 

 be carried to a great extent. It is termed orgasm, and when it becomes painful and 

 permanent, injlammatioa. The irritation may also originate iu the nerve, vdien it 

 experiences acute sensations. 



This mutual influence of the nerves and fibres, either in the intestinal sj-stem, or in 

 the arterial system, is the real sparing of vegetative life in animals. 



As each external sense is permeable only by particular kinds of sensation, so 

 each internal organ may be accessible only to such or such agent of irritation. Thus, 

 mercury irritates the salivary glands, cantharides excite the bladder, &c. I'hese 

 agents are what are termed specifics. 



The nervous .system being homogeneous and continuous, local sensations and irrita- 

 tion debilitate the whole ■ and each function, carried too far, may enfeeble the others. 

 Excess of aliment thus weakens the faculty of thought ; while prolonged meditation 

 impairs the energy of digestion, &e. 



Excessive local irritation will enfeeble the v\diole body, as if all the powers of life 

 were concentrated on a single point. 



A second irritation produced at another point may diminish, or divert as it is termed, 

 the first; such is the efli'ect of purgatives, blisters, &c. [denominated counter-irritation]. 



All rapid as the foregoing enunciation is, it is sufficient to establish the possibility of 

 accounting for all the phenomena of physical life, by the simple admission of a fluid 

 such as we have defined, from the properties which it manifests.! 



• Tn Ihc rtbove sentence, there are 'listinctlv mentioned tlie three I John Herschel, " (fnr ivliich \vnn(]erfullv con5litutefi orjan no other 



sorts of nerves, the separnte functions of wliieh have been con- mode of action ijossessinf,' the least probability has ever been devised), 

 clusively demonstrated by Sir Charles Bell: viz., nerves of rotil'wt), \ be an electric pile, constantly In action, it maybe conceived to dis- 



vvhieh transmit the mandates of the will ; of sejisfitlori, which convey cbartre itself at regular intervals, when the tension of the electricity 



to the sensoriuin the impressions of the senses: rqA of eyiiputhy, developetl reaches a certain point, along the nerves which eommn]:i- 



or involuntary movement, the reunion of the ramifieations of which eate with the heart, and thus to excite the pnlsatii>ns of that organ, 



in a plexus of knots, or gaof^lions, is intimated in the text, those of This idea Is forcibly suggested by a view of that elegant apparatus, 



the second class being distinguished by a swelling or ganglion near the dry pile of Deluc. in which the successive accumulations of 



their base— F.D. electricity arc carried otT by a suspended ball, wliich is itept, by the 



t The unceasing chemical changes consequent upon vitality must discharges, in n state of regular pulsation for any length of time. We 



necessarily dcvelupe electricity ; and that the nervous Jliiid is no other have witnesseii the action of such a pile, maintained iti this way for 



than the ele.r.lrii:, may be considered as proved by the identity of their whole years, in the stody of the above-named eminent philosopher, 



phenomena. Indeed, it has long been known that the transmission The same idea of the cause of the pulsation of the heart appears to 



of voltaic electricity along the nerves of a recently dead animal, have occurred to Dr. Arnott, and is mentioned in his useful and ex- 



Bulbces to produce the most violent muscular action [ but the regula- cellent work on Physics, to which, however, we are not indebted for 



tiun of that action, its exclusive direction to particular soites of the suggestion, it having occvirred to us independently manv years 



Lauseles, rciuires the vital impulse. "If the brain," remarks Sir ago."— Z^isc '.ar.^c or, //:,■ ,S/ar/y o/ .V„/,;r.,/ /-'/n7„s..;,/,y, p.' 3-i;j.— 1.:d. 



