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INTRODUCTION.

I. OF THE BRAIN, AND NERVOUS SYSTEM.

May not animals have a power of extracting from the blood the ele&trical fluid ? The Brain then would be the great laboratory for this purpose.

PRIESTLEY.

Most authors have supposed, that the nerves are tubes or ducts conveying a

fluid secreted in the brain, cerebellum, and spinal marrow. But, of late years, several ingenious physiologists have contended, that a secreted Avid Was too inert for serving the offices performed by the nerves, and, therefore, fuppose they conduct a Huid the same as, or fimilar to, the ele&rical fluid. Two arguments chiefly seem to conduct them to this conclusion. The nervous energy appears to them to be moved with prodigious velocity. Baron de Haller observes how often a muscle of any diftant part could act in a minute ; and supposing that, previous to every contraction, the nervous fluid moved from the brain to that part, he calculates its motion at 9000 feet the first minute. The other principal argument is more direct, and has been thought very conclufive; to wit, that some animals, as the Torpedo, and Gymnotus electricus, have the power of giving an electrical shock, and that, on diffecting them, a piece of machinery, proper to them, is discovered, consisting of very LARGE NERVES.

MONRO.

It would be foreign to this publication to enter here into a minute description of the BRAIN, the MEDULLA SPINALIS, and the Nerves which proceed from thence, Vol. IV.

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affording sensation and motion to the different parts of the animal frame. Suffice it then to say, that these are composed of two distinct parts;

1. The CORTICAL PART, or VASCULAR; and

2. The MEDULLARY, or FIBROUS:

Which parts are invested by their proper membranes, called the pia, and DURA, MATER.

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The OUTER OR CORTICAL PART of the brain, spinal marrow, and nerves, are exceedingly vascular. RHUYSCH has made this very evident by his preparations. After a successful injection of his ceraceous matter into the carotid arteries, he found the cortical part of the brain became red; then separating a red portion of it from the rest, but cohering with the branch of an artery, and macerating it in water, till the membranes putrified and difsolved off, he put what remained in spirits of wine, and found it to be red, very tender, flocculent, a fleecy, coherent substance, filled and tinged red, as far as the injection had reached; the oily nature of which had hindered it from being dissolved in water, as the membranes, and other parts that were not filled, had been.

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