Small Books on Great Subjects (Volume 1-2)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1845. Excerpt: ... papillae easily detached, and which appear to close the ends of the hollow fibres. The audi PORTION OF THE OPTIC NERVE MAGNIFIED. tory nerve has something of the same appearance, though the fibres are less minute than those of the optic nerve, and the points which show themselves on the membrane they penetrate, differ slightly from these in their form. It seems probable that both these nerves are destined to receive impressions from different undulatory movements, the one conveying the sensation of light, the other of sound; and though it would be presumptuous to say that the modus operandi can be certainly or distinctly stated, yet a very simple illustration may perhaps give some notion of it to those who have not time to pursue the study further. When a hollow tube is filled with liquid, the slightest pressure at one end is instantly perceived at the other. If, then as modern observers assert, the nerves be hollow fibres filled with a half fluid substance which may be seen issuing from them if divided, then it is easy to comprehend that the impression made at one end of the fibril may be conveyed through every fibril connected with it down to the extremest point of the motor nerves. What the difference of structure is, which makes this impression in the one instance convey colours, in another sounds, and, when propagated further, produces that irritation of the muscles which causes movement, has as yet eluded observation; but it is evident from the result, that some decided difference must exist. Time was, indeed, when the nerves of the senses were looked upon as mere passive conductors, through which the impressions made by the properties of bodies were supposed to be transmitted unchanged to the sensorium. More recently, physiologists have begun to a...