Such preparations RHUYSCH often made, and found the experiment fucceed in like manner with the CEREBELLUM, SPINAL MARROW, and NERVES.

Now we have before fhewn, that in every contraction of the heart, a very large quantity of blood was fent 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 fends to the brain one fixth of the whole mass of blood, MONRO at lefs. Let us therefore suppose, that the quantity thrown out by the left ventricle, at every pulfe, is only one ounce and a half, which is a very low value, as the exacteft and latest measures of the capacity of the ventricle run from one to three ounces. A fixth part of this is a quarter of an ounce. Let us take the number of pulfes to be 60 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 muft 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 fo great a quantity of blood arrives at the brain in fo fhort a space of time oxygenated (and though it were taken double, there would be no great exaggeration of the matter), and paffes thence unoxygenated, is it not reafonable to fuppofe, that in the subtle vascular texture of the CORTICAL SUBSTANCE there is ftrained off, or fecreted from the arterial blood brought to it, a fluid, the finest, most attenuated, and moft moveable in all the animal, body, and analogous to the matter of fire, or the electric fluid and fince the MEDULLARY SUBSTANCE of the brain is of a fibrous compofition, the threads of which are disposed in a parallel direction (as is particularly obvious, even to the naked eye, in the corpora ftriata, the thalami of the optic nerves, especially of fifhes, in the fornix and other parts of the brain when immersed in the nitrous acid), does not this fubtle and penetrating fluid therefore cling to the MEDULLA, and pass along the NERVES at the command of the will, which are evidently of the fame texture as the brain, just as the electric fluid is retained by the main conductor, and paffes along a wire connected to it? If fo, we have answered the question proposed by Sir Ifaac NEWTON, "Is not Vifion pro"duced by the ethereal fluid, or fomething analogous to "this medium, excited in the bottom of the eye by

"the

"the impulse of light, and propagated along the folid, "pellucid, and uniform fibrille of the optic nerves to "the place of fenfation?"-" And is not Hearing per"formed by the movement of this or fome other ana

፡፡

logous fluid, excited in the auditory nerves by the "percuffion of the air along the folid, pellucid, and "uniform fibrilla of thofe nerves into the place of fen"fation, and fo of the other fenfes ?"-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 fibrilla of the nerves into the "muscles for contracting them?" If so, these threads or fibres called NERVES are fo many electric conductors. The electricity of each fibril is excited apart, and each apart impreffes a ftroke upon the brain, which is proportioned to the impulfion they receive, and to the excitement of the electric matter. In this cafe, every nerve excites diftinct impreffions.

Not only feveral im

preffions are made at the fame 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 fucceffion, very diftinctly, in the space of a quarter of a fecond. Between

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 fenfation remains for a fhort time after the object is gone. Thus, to use again the expreffions of the immortal NEWTON, "If a ftick 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 fenfation of the "burning body, in the several places of that circle re"mains impreffed upon the brain until the burnt end "return again to the fame place. And fo in the quick "confecution of colour, if all the feveral 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 impreffion of every colour re"mains on the fenforium, until a revolution of all the "colours be completed, and that first colour return "again. The impreffions therefore of all the fucceffive "colours are at once in the fenforium, and beget a fen"fation of white." Thus alfo common electricity has a loitering pace, not eafily reconcileable with its common immeasurable velocity.

The caufes which excite fenfation being without the body;

body; to wit, the objects of the five fenfes; and exter nal with respect to the medullary part of the brain, is it

not reasonable to infer, that fenfation is produced by the

reflux of the electric or nervous fluid moving along the

nerves towards their origin, occafioned by the impulse of its objects or causes? Or is this fluid expended, and drawn off, and fenfation the refult of the determination of the electric, or nervous fluid, to the part stimulated? i In the exercise of voluntary muscular motion, it is no lefs natural to conclude, that the electric fluid is, by an effort of the mind, operating in a manner instantaneoufly, fent from its origin in the beginning of the medullary part, along the nerves, which are continued into the mechanism of the muscles.

With refpect to the operations of the mind or foul, as will, confcioufnefs, memory, imagination, judgment, &c. it is reasonable to fuppofe, 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 mafterpiece of creative skill. We fee 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 fome grains of opium, entirely change our manner of feeing things, and confequently,

of