IRRITABILITY, AND MUSCULAR POWER. 107 



repairing and augmenting them."* Yet, when we come to examine into the 

 subject more closely, we find that all these terms, so expressive of a specific 

 being and distinct reality this ESSENCE that VIVIFIES and ANIMATES, has neither 

 being, nor essence, nor vivification, nor animation, nor reality of any kind 

 that the whole of these expressions are metaphysical ; and that the word 

 VITAL PRINCIPLE is not designed to express a distinct being, but is merely an 

 abridged formula, denoting the TOTALITY OF POWERS ALONE which animate liv- 

 ing bodies, and distinguish them from inert matter, the TOTALITY OF PROPERTIES 

 and LAWS which govern the animal economy.f So that we have here not only 

 the employment of terms that have no meaning, but properties and laws, 

 powers and principles, without any source, a superstructure without a foun- 

 dation, effects without a cause. 



But what is this curious and delicate instrument itself? this machine that 

 so nicely responds to the impressions communicated to it, and visibly enve- 

 lopes so invisible a constituent ? 



It is not my intention in this series of popular study to enter into any mi- 

 nute history of the animal frame, but shall confine myself to those general 

 views of it which are requisite to show by what means it is operated upon 

 by the delicate powers we have just contemplated, and the more curious phe- 

 nomena which result from such an impulse. 



The animal frame, then, is a combination of living solids and fluids, duly 

 harmonized, and equally contributory to each other's perfection. The prin- 

 ciple of life, whatever it consists of, exists equally in both ; in some kinds in 

 a greater, in others in a less degree. In the fluids, Mr. Hunter has traced it 

 down to their first and lowest stage of existence, for he has traced it in the 

 chyle ;J and there are evident proofs of its accompanying several of those 

 which are eliminated from the body ; in the blood it is found, as we have 

 already had occasion to notice, in a high degree of activity, and probably in 

 a still higher in the nervous fluid. 



In the solids it varies equally. There are some in which it can scarcely 

 be traced at all, excepting from their increasing growth, as the cellular mem- 

 brane, and the bones ; in others, we find a perpetual internal activity, or sus- 

 ceptibility to external impressions. But it is in those irritable threads or fibres 

 which constitute the general substance of the muscles or flesh of an animal, 

 that the principle of life exerts itself in its most extraordinary manner, and 

 which it more immediately, therefore, falls within the scope of the present 

 lecture to investigate. 



The muscle of an animal is a bundle of these irritable fibres, or soft, red, 

 cylindrical, and nearly inelastic threads, formed out of a substance which the 

 chemists, from the use to which it is applied, denominate fibrine ; and which, 

 when examined microscopically, are seen to divide and subdivide, as far as 

 the power of glasses will carry the eye, into minuter bundles of fibrils, or still 

 smaller threads, parallel to each other, and bound together by a delicate cel- 

 lular web-work, obviously of a different nature. They are uniformly accom- 

 panied through their course by a number of very minute nerves, which are 

 chords or tubes that originate from the brain, and branch out in every direc- 

 tion, either immediately from the brain itself, or from some part of the spinal 

 marrow, which is a continuation of this organ ; by which means a perpetual 

 communication is kept up between the sensorium and the remotest part of 

 the body, as we shall have farther occasion to notice hereafter.^ Upon the 



* " Perspnne aujourd'hui ne conteste I'EXISTENCK D'UN PRINCIPE DE VIE qui soumet les etres qui en 

 jouisscnt a un ordre de lois differentes de celles auxquelles obeissent les Sires inariimes, force a laquelle 

 on pourroit assignor, comme principaux caracteres, de soustraire les corps qu'Ei.LK ANIME, a 1'empire absolu 

 des affinites chimiques, auxquelles ils auroient tant de tendance a ceder, en virtu de la multiplicite de leura 

 elemens ; et de maintenir leur temperature a un degre presque egal, quelle que soit d'ailleurs celle de 1'at- 

 mosph^re. Son ESSENCE n'est point de conserver 1'aggregation des molecules constitutives, mais d'attirer 

 d'autres molecules qui, s'assirnilant aux organcs qu'ELLE VIVIFIE, remplacent celle qu'entratnent les pertes 

 journalises, et sont employees a les nourrir et a les accroltre." Nouveaux Elemtns de Physiologic, torn. i. 

 p. 81. Paris, 8vo. 1804. 



"Le mot de PRINCIPE VITAL, force vitale, &c. n'exprime point un etre existant par lui-meme, et inde- 

 pendammcnt des actions par lesquelles il se manifesto : il ne faut 1'employer que comim une formule abregee 

 dont on se sert pour designer 1'ensemble des forces qui animent les corps vivans et les distingucnt de la 

 matiere inerte : 1'ensemble des proprietes et des loix qui rgissent 1'economie animate." Ib. p. 80 



t On the Blood, p. 91 Series i. Lecture iv. 



