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Such preparations Rhuysch often made, and found the experiment succeed in like manner with the CEREBELLUM, SPINAL MARROW, and NERVES.
Now we have before thewn, that in every contraction of the heart, a very large quantity of blood was sent almost in a straight line from the heart, and therefore the blood, from its proximity to the brain, must move with a proportionate velocity. HALLER computes that the heart sends to the brain one sixth of the whole mass of blood, Monro at less. . Let us therefore suppose, that the quantity thrown out by the left ventricle, at every pulse, is only one ounce and a half, which is a very low value, as the exactest and latest measures of the capacity of the ventricle run from one to three ounces. A fixth part of this is a quarter
Let us take the number of pulses to be 6o in a minute, or 3600 in an hour, which is a very flow pulse. By this estimate, 900 ounces, or fix pounds and fix ounces, of oxygenated or arterial blood must arrive at the cortical
part of the brain in an hour, which amounts to 110 pounds in the natural day to be returned to the four jugulars back again to the heart unoxygenated *.
* Vide the Map of the Heart, Vol. I. p. xxiii.
As so great a quantity of blood arrives at the brain in so short a space of time oxygenated (and though it were taken double, there would be no great exaggeration of the matter), and passes thence unoxygenated, is it not reafonable to suppose, that in the subtle vascular texture of the CORTICAL SUBSTANCE there is strained off, or secreted from the arterial blood brought to it, a fluid, the finest, most attenuated, and most moveable in all the animal body, and analogous to the matter of fire, or the eleetric fluid ? and since the MedULLARY SUBSTANCE of the brain is of a fibrous composition, the threads of which are disposed in a parallel direction (as is particularly obvious, even to the naked eye, in the corpora striata, the tha-, laini of the optic nerves, especially of fishes, in the fornix and other parts of the brain when immersed in the nitrous acid), does not this subtle and penetrating fluid therefore cling to the MEDULLA, and pass along the NERVES at the command of the will, which are evidently of the same texture as the brain, just as the electric fluid is retained by the main conductor, and passes along a wire connected to it? If so, we have answered the question proposed by Sir Isaac Newton, “ Is not Vision pro“ duced by the ethereal fluid, or something analogous to “ this medium, excited in the bottom of the eye by
" the impulse of light, and propagated along the solid, “pellucid, and uniform fibrillæ of the optic nerves to
the place of sensation ?"_" And is not Hearing per“ formed by the movement of this or some other ana
logous fluid, excited in the auditory nerves by the "percussion of the air along the solid, pellucid, and “ uniform fibrillæ of those nerves into the place of sen" sation, and so of the other senses ?” - And again,
Is not animal Motion performed by the motion of this “ medium, excited in the brain, by the power of the
will, and propagated from thence along the folid,
pellucid, and uniform fibrillæ of the nerves into the " muscles for contracting them ?" If so, these threads or fibres called NERVES are so many electric conductors, The ele&tricity of each fibril is excited apart, and each apart impresses a stroke upon the brain, which is proportioned to the impulsion they receive, and to the excitement of the ele&tric matter.
In this case, every nerve excites distinct iinpressions. Not only several impressions are made at the same time, but they are effected with a rapidity that refutes the idea of fluggish matter, and which belongs uniquely to the electrical fluid. One may hear three or four founds in succeffion, very distinctly, in the space of a quarter of a second. Between 8
the time of touching a body, and the consciousness of it taking place, there is scarce any intermediate space which can be calculated by the known measures of time. However the sensation remains for a short time after the object is gone. Thus, to use again the expressions of the immortal NEWTON, “ If a stick burnt at one end be
nimbly moved round in a circle, with gyrations con“'tinually repeated, the whole circle will appear like “ fire; the reason of which is, that the sensation of the “ burning body, in the several places of that circle res mains impressed upon the brain until the burnt end s return again to the same place. And so in the quick « confecution of colour, if all the several colours into " which light may be divided by the prism, be painted
on a card in their due proportion, and whirled round " any pointed body, the impression of every colour re6. mains on the sensorium, until a revolution of all the " colours be completed, and that first colour return
again. The impressions therefore of all the successive " colours are at once in the sensorium, and beget a sen« fation of white.” Thus also common electricity has a loitering pace, not easily reconcileable with its common immeasurable velocity. The causes which excite sensation being without the
body; body; to wit, the objects of the five senses; and exter, nal with respect to the medullary part of the brain, is it not reasonable to infer, that sensation is produced by the reflux of the eletric or nervous fluid moving along the ņerves towards their origin, occasioned by the impulse of its objects or causes? Or is this fluid expended, and drawn off, and sensation the result of the determination of the eleElric, or nervous fluid, to the part stimulated ? i
In the exercise of voluntary muscular motion, it is no less natural to conclude, that the elettric Auid is, by an çffort of the mind, operating in a manner instantaneously, sent from its origin in the beginning of the mea dullary part, along the nerves, which are continued into the mechanism of the muscles.
With respect to the operations of the mind or soul, as, will, consciousness, memory, imagination, judgment, &c. it is reasonable to suppose, that these are attended with respectively different motions of this fluid, separated from the CORTICAL and attracted by the MEDULLARY PART of this wonderful organ, the masterpiece of creative skill.; We see this verified every day, when more or less of stimulating food, altering the action of the heart, a few drops of a certain liquor, or some grains of opium, entirely change our manner of seeing things, and consequently,