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tient and rational faculty, all intimately connected, yet each apparently distinct from the other.
So intimate, indeed, is the connection as to impose on us the opinion of their identity. The body springs and bounds as though its inert fabric were alive; yet have we good reasons for believing that life is distinct from organization. The mind and the actions of life affect each other. Failure or disturbance of the actions of life prevent or disturb our feelings, and enfeeble, perplex, or distract our intellectual operations. The mind equally affects the actions of life, and thus influences the whole body. Terror seems to palsy all its parts, whilst contrary emotions cause the limbs to struggle, and become contracted from energy. Now though these facts may countenance the idea of the identity of mind and
life, yet have we good reasons for believing that they are perfectly distinct. Whilst, therefore, on the one hand, I feel interested in oppugning those physiological opinions which tend to confound life with organization ; I would, on the other, equally oppose those which confound perception and intelligence with mere vitality.
In the first lecture I endeavoured to shew that Mr. Hunter's Theory of Life was verifiable, and that it afforded the most rational solution of the cause of irritability, which had hitherto been offered to the public. It now appears that it does not essentially differ from that of the best physiologists, with regard to the explanation it affords of the nervous functions. As it is impossible to review all the phænomena of these functions in a lecture, I shall on the present
occasion merely direct your attention to the consideration of one other subject, which is, the opinions we may be warranted in forming, respecting the connection of irritability and sensibility.
This subject has been the cause of much controversy.
Haller maintained that irritability was a distinct property. inherent in muscles ; to use his own words, that they had a vis insita, independent of the vis nervea; which opinion has of late received additional corroboration from some experiments of Mr. Brodie. Those who object to this opinion, can, I think, only oppose it on the following grounds. They must contend either that the muscles have a kind of perception of injury which causes them to contract, even though they are unconnected with the brain; or that the nerves are the organs, which prepare and supply the muscles with
something which is the cause of irritability.
Concerning the first of these suppositions, that muscles may have a perceptibility of injury, distinct from that which we understand to be feeling, I have to observe, that we can have no idea of sensation but what results from our own experience, which may be defined to be perception attended with consciousness; which kind of sensation is confined to the brain alone. Of any other kind of perception, it is evident we can never form any idea.
If a man's leg be amputated, and by voltaic electricity I excite contraction in its muscles for some hours, how can I know whether they feel or not? We naturally judge of other subjects from ourselves, and knowing that we shrink from
whatever pains us, some persons seem to conclude that the muscles contract because they have been hurt. To the patient who has suffered amputation, such a supposition would seem absurd. He
may feel pain when no stimulus is applied to the limb, or he may feel case when it is. Nay, he continues to feel pain, or sensations, in the limb when it is rotten, or no longer in existence ; which seems to shew the integrity of the
of the sentient principle remaining in the brain.
In vegetables, and in some moluscæ, no traces of a nervous system are discoverable, yet the irritability of life is manifest in all. In the ascending series of animals, in proportion as the brain becomes large and complex, we have evidence of the perceptions and intelligence increasing ; a circumstance which would lead us to believe that these faculties were connected