"The negatio formalis is destroyed or abolished in any case of impression communicated to the sensorium. Natural perception, in its ratio positiva, is not abolished or degraded by being converted into sensation, but is rather exalted, or gifted with a more dignified nature. By as much as public or general knowledge is preferable to private, or public advantage to that of an individual, by so much is sensation preferable to natural perception. Hence nature formed so many organs of sense, that the phantasy might have notice of what ought to be done, desired, or avoided." He does not doubt that external sensibility is inherent in the nervous parts of the external organ, whence he infers that it may readily incite the fibres of such organ ad appetendum et movendum; for, as external sensation is communicated to the brain by means of the nerves, it must of necessity be true, that these nerves and nervous parts (such as the fibres,) are the subjects of it. Since then sensibility causes its subject to feel, it consequently enables it to desire and move comformably. For perception in any subject is vain, unless it can desire, and appetence is useless, unless it can move. External sensibility, therefore, may be said to render the fibres _actu irritabiles_, for example, as often as the irritating cause is perceived; but as the irritation is perceived, not by a sensibility, but by a mere natural perception, this it is which constitutes their irritability. Thus we may perceive that the triunit consisting of perception, appetence, and motion, constitutes the celebrated irritability of our author. But he has been too latitudinarian in his application of the theory; for he did not limit it, as HALLER has subsequently done, to one sort of fibres, or indeed to fibres alone, for he says in cap. IX., "It is to be remarked that natural perception belongs to other parts of the body besides fibres; to wit, to the parenchymata, bones, marrow, fat, blood, recrementitious juices, humours of the eye, and such like, all which are irritable, and increase the irritable constitution of the parts, but these parts hardly admit of the existence of animal perception." HALLER blames GLISSON for having gone so far in his application of the theory, and it is well known that he himself restrained it to the single tissue of muscular fibres, and denominated it vis insitum, or inherent force; whereby he distinguished it from his vis mortua or elastic contraction, on the one hand, and the vis nervosum or voluntary power, on the other; the former being something less, and the latter something more than irritability. GLISSON'S theory, when fully explained, which we cannot for want of space do here, will be found to bear a very strong resemblance, in many points, to that of BICHAT, who has invested the matters of the body with vital powers, far beyond those attributed by HALLER; and as we are not furnished in the present article with sufficient space, we hope in some subsequent