Brain, in anatomy, a great viscus in the cavity of the skull, of an. oval figure, and larger in man, in proportion to his size, ' than in any other animal. The brain is uniformly considered as the grand sensorium of the body, or the organ of all the senses ; and hence it is supposed, not without reason, to be the seat of the soul. The most important functions of an animal body are those of the brain. To afford a more distinct view of the subject, we shall mention a few experiments which have been made upon animals.

If the brain be irritated, dreadful convulsions take place all over the body. If any part of the brain be compressed, that part of the body which derives its nerves from the compressed part, is immediately deprived of motion and sensation. On compressing, tying, or dividing a nerve, the muscles to which the nerve proceeds, become paralytic. If the nerve thus compressed, tied, or divided, had before any particular sensation, it exists no longer; but, on removing the compression, or untying it, its peculiar sense returns.

From these phenomena, it is evident, that every sensation in an animal body is derived from the brain, or from the spinal marrow, which is a continuation of the brain; and that it is conveyed thence, through the medium of the nerves, to all parts of the sentient body. But, in what manner the various sensations are produced by the nerves, and how the will operates upon the contiguous and remote organs, so as to put them into instantaneous motion, are difficulties which have never been satisfactorily explained, and, in all probability, will always baffle the keenest investigation.

As the brain is the representative organ of the mind, its sound and perfect state is of the utmost importance in the exercise of the intellect. If, therefore, the brain of an individual, be preternaturally soft, or too firm and hard, or specifically too light, or proportionately too small; or if it be in any manner compressed or shaken by external violence; or if acrimonious humours should settle on it, in consequence of various diseases; or, lastly, if in plethoric habits too great a portion of blood should flow towards the head, and too much extend its vessels ;—in all these cases, the representing faculty will morn or less partake of the disorder. Thus, the power of imagination, or fancy, is sometimes so much increased, that the patient is either in part, or entirely, deprived of the faculty of judgment. Such, for instance, is the case in delirious persons, who are then only called maniacs, when a total privation of their reasoning faculty is evident. In ideots, or stupid people, however, the mental disease arises chiefly from their incapacity of comprehending and properly arranging ideas.

The causes of these humiliating derangements of the human mind, though various, may be reduced to the following heads : namely, inordinate passions, especially those which are attended with a great dissipation of strength ; debauchery of every kind ; an irregular mode of life , excessive eating and drinking; intense, as well as long-continued application to study; and likewise, a sudden change of climate, air, and aliment.

It deserves to be pointed out as a vulgar error, that abscesses of the brain discharge themselves through the mouth and ears ; and that snuff is liable to enter into the brain; neither of these is capable of passing through that bone, which has the form of a sieve ; nor is any matter, or fluid, secreted in a common cold, evacuated by that canal, though discharged through the nostrils. The seat of this disease is, indeed, not in the brain, but in the cavities of the nose ; and if im-posthumes take place in the ear, they suppurate and empty themselves externally.

Inflammation of the Brain, is a disease more common in hot than in temperate climates : in the latter, however, it may also take place from external violence, or in consequence of severe falls, blows, and bruises upon the head ; night-watching ; hard-drinking; strong passions, especially those of grief, anger, and anxiety ; exposure to the heat of the sun during sleep, with the head uncovered, etc. The principal symptoms of this dangerous malady are, pain of the head, redness of the eyes, want of sleep, and slight dropping of blood from the nose : these are attended with costiveness and a retention of urine. As the disease, when neglected, is often fatal in a few days, medical advice should be called in without delay. Meanwhile, the patient ought to be kept as quiet as possible, and free from the access of strong light; his body must be kept open by clysters ; the legs bathed in warm water ; the bleeding of the nose promoted by warm fomentations to the part; and the head, after being shaved, should be frequently rubbed with vinegar and water ; or cloths dipped in the following solution may be applied, and repeated every hour, or half hour, with the best effect. Take two ounces of nitre, and one ounce of sal ammoniac, dissolve them in five pints of water and half a pint of strong vinegar. Of this mixture the patient may also drink a table spoonful every hour, or oftener.