Part 4

By the intellectual functions, I understand the actions of the intellectual organs, or, in other words, those actions which constitute mind. With soul—the sacred and revered province of theologians, I do not wish in the slightest degree to interfere; not for the harsh reason assigned by atheists, namely, that the whole empire of ignorance, the direction of the basest passions, and the gun or bayonet of the soldier are under their command (these are sentiments which I never shall profess), but for a juster and a better reason, namely this, that soul is, in truth, their proper province.

Sensation, then, seems to be entirely dependent on touch, which, in the other senses, is only modified so that one receives one kind of it, and another receives another; thus the tongue is touched by means of liquids, the nose by means of odours, the ear by aeriform vibrations, and the eye by light.

All the other intellectual functions are nevertheless mere modifications of sensation. Upon them, therefore, we shall not dwell, but, by taking into view some important facts in anatomy, which have a relation to all of them, I shall be able to explain sensation in particular.

Sommering has observed, that man has the largest brain in proportion to the nerves given off from it; and that this proportional magnitude, may, in every instance, be referred to as the best criterion of the degrees of intelligence. Now, it appears to me not at all difficult to account for this fact (the general truth of which may be granted), by comparing it with another not less important, viz. that, in the inferior classes of animals, the nervous system becomes, as you descend, more and more widely diffused.

Hence, I deduce this important principle, viz. that the degrees of intellect are, in all animals, in exact proportion to the concentration of the nervous system.

Now, the more equally distributed this system is, the more independent of each other are the parts of organized beings, or, in other words, the necessity of a connection of these parts increases, in proportion to the magnitude of the common trunk compared with the rami. It is only, therefore, in the more perfect animals, that the connection of the different parts of the nervous system, and particularly the presence of central parts, is necessary to the existence of the different functions.

Animals, on the contrary, having this sensitive substance very generally diffused, when mutilated, recover their figure, or, when cut into pieces, form several individuals, having each a system of sensation and volition. The larger warm-blooded animals acquire pieces of flesh analogous to those which have been cut away; crabs acquire new claws; the tadpoles of frogs and water newts acquire new limbs and tails; and the lower end of the snail, having been divided from the upper, acquires a new head. The earth and boatworm, when divided into considerable pieces, form several new individuals; but animals having this system still more generally diffused, as the polypus, when divided into the smallest fragments, each fragment self-exists and becomes a perfect individual.

This also is more or less the case with plants. As you descend among them, their parts become less dependent on each other. The dicotyledons, which possess irritability, sleep and the principle of life most diffused, and which, among plants, are analogous to the dicordated animals, namely quadrupeds and birds, possess concentric fibres and the most diffused sensibility; the monocotyledons, analogous to the monocordated animals, namely reptiles and fishes, possess more numerous centers and less diffused sensibility; and the acotyledons, analogous to the acordated animals, possess most numerous centers and least diffused sensibility.

As, in some worms and zoophytes, there is indeed no appearance of nerves, and certainly none in plants, which yet possess sensibility, all this gradually approaches to the attraction and repulsion of the magnet and electrics, which, like some of these, are divisible almost to infinity, and yet possess their various powers, which, like the sensibility of the superior animals, connected by nerves, are only evidenced when led by conductors.

Hence, I conclude, that sensation, understood in this limited sense, as distinct from perception, and differing, toto coelo, from soul, is, like extension, an imprescriptible property of all matter: but it may exist in as many forms and as many relations as it; in its separate particles; in larger combinations, as polypes; in still larger ones, as worms and insects, where these extended and sentient particles, connected by nerves, have more extensive relations and more complete dependence on each other; or uniting to constitute perception in whole bodies, as in the more perfect animals, where a sensorium commune exists, and where, in consequence of the most exquisite arrangement, and the finest relations, no particle can be deranged without affecting all the rest.

It is indeed, these various degrees in which it appears, that afford a strictly analogical proof of its existence as a primary property of matter.

As man then has not only sensation in the separate parts, but perception arising from the whole, the descent is gradual to beings which have merely sensation in distinct parts, but no general perception; and thence equally gradual to beings which have sensation limited to their individual particles.

Now, as the perceptions of two of the superior animals cannot unite to form one perception, so the sensations of two parts of a polyp cannot combine in perception; nor is it of course more wonderful, that the sensations of two of the minute particles of matter cannot unite in one common sensation.

As we do not expect electricity to be evidenced without conductors, why should we expect sensation, in any great degree, without those nerves which are its conductors? It would be as irrational to deny the former, when conductors are not present, as to deny the latter (understood as I have defined it), when nerves are absent.

Neither is it more wonderful that these sensations, thus limited, are not evidenced; because it is scarcely to be expected, that the functions of that should be evident, the absolute structure of which is unknown, and because it is exactly in proportion to the concentration of sensation (and by no means to its division) that it is, at any time, evidenced.

Upon the same principle, it is, that the particles of a pigment, when in contact, are more evident than when extended over an immense surface, or that a combination of pullies and one cord produce more evident motion than each of them, with separate cords, could separately. But it is unnecessary to accumulate illustrations—the principle pervades all nature, and every natural operation illustrates it.

Nor do we merely find evident sensibility thus produced by the various arrangements of matter: it is implicitly dependent on all the changes of bodies, and is identified with their motions, by being suspended whenever these are suspended. Of this, the hybernation of animals, the winter state of most plants, the state of the embryo in utero or in ovo, of the chrysalids of insects, the nymphs of worms, and the seeds of plants, afford examples.

Nor is this all: but evident sensibility may be produced and destroyed at pleasure by a mere alteration in the arrangement of the particles of one and the same body; as in the wheel animal, and the anguillæ of tiles.

Nor is even this all: you may, if you choose, by the mere arrangement of the particles of matter, as I shall afterwards prove by experiment, at once produce myriads of animals, and bestow upon them motion, or in other words, the phenomena of sensibility. This, the experiments of Spallanzani, contrary to his own inclination, decidedly prove.

If it be objected, that it may be as fairly argued, that sensation is something combined with these forms of matter, I answer, that we are not entitled to suppose any thing an independent being which never appears but in combination.

Now, as we have shown that sensation is implicitly dependent upon, or connected with motion; and as this and all the other functions of the brain, are entirely the results and modifications of sensation, they also must be dependent on or connected with motion.

Far be it from me to pretend to account for mental operation by mere physical motion. But, that motion accompanies all these processes, I am certain; nor can the supposition that motion is made use of in the most mysterious operations of the mind, possibly detract from the honour of a Deity, or from our admiration of natural operations.

We have little need to be afraid of a moderate and rational materialism. It is the idealism of Berkeley, it is the scepticism of Hume—those dangerous opponents of such materialism, that have so deeply injured philosophy and religion. It is according to these systems, that prophets, apostles and miracles, are only ideas in the mind; and, indeed, the unreasonable dislike to a rational materialism, is alone chargeable with having led to the dangerous scepticism of Hume.

That physiologists, then, should so long have permitted others to encroach upon their proper province, is disgraceful to them, and has been most mischievous to science. To this is owing the barbarism of the doctrine of mind. As physiologists abandoned it, philosophers found it difficult to give it a name.—Some called it morals—others metaphysics—and others, the philosophy of the mind. But I have just endeavoured to shew, that it is neither morals nor metaphysics, nor the philosophy of the mind—but the philosophy of the intellectual organs of the human body.

FIRST PRELIMINARY LECTURE TO THE COURSE OF PATHOLOGY AND THE PRACTICE OF MEDICINE; EXHIBITING THE OUTLINE OF A NATURAL SYSTEM OF PATHOLOGY, MEDICINE AND THE MATERIA MEDICA.

GENTLEMEN,

I shall not, on the present occasion, detain you with prefatory remarks; but, as a fairer proof than any I can adduce, of the necessity of such a course of lectures as I now propose, shall merely repeat to you, upon this subject, the sentiments of one whom genius in the science and skill in the art of medicine have elevated high in his profession, and whose eloquence is not less admirable than his professional abilities.

“To ally anatomy,” says he, “more closely with surgery, to connect the art more intimately with the science from which it flows, seems to me a task as yet imperfectly accomplished, though of the very highest importance.—Anatomy is not made interesting to the pupil as the basis of our reasoning on disease, the rule of our prognostications, the sole guide in operating: He is taught to know the parts and remember their names, and then he is dismissed from the school; and of this school we are all pupils, abandoned early in our career, left to learn, in the hurry of practice, the very principles of the science!—The anatomy of surgery differs widely from that taught in the schools.—Pathology, which ought to unite science with art, is a sort of neutral ground betwixt the two provinces of anatomy and surgery, little regarded on either hand.”