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dimenfions, and obedient to the fame laws, clearly proves that they both depend on the fame caufe. The living principle, therefore, in the blood, which I have endeavoured to fhew to be fimilar to the living principle in the folids, owes its exiftence to the same matter which belongs to the other, which is the materia vite diffufa, of which every part of an animal has its proportion: it. is as it were diffused through the whole folids and fluids, making a neceffary constituent part of them, and forming with them a perfect whole; giving to both the power or susceptibility of impreffion; and, from their conftruction, giving them confequent reciprocal action,

SECT.

SECT. XXXIV.

OF OXYGEN AS RELATED TO SENSIBILITY.

THERE is no doubt but that sensibility refides in the nerves, as irritability does in the contractile fibre; but fince both fenfibility and irritability are fufpended by fubmerfion, and only reftored by the blood receiving the oxygen principle from a pure refpirable air, may we not from thence infer that they depend both for their powers of action on the fame caufe?

We obferve that where it is intended that nerves shall convey impreffions with great accuracy, as in all the fenfes, the diftribution of blood-veffels is more profuse than in almost any other equal part. When the white of the eye gets inflamed and fuffufed with arterial blood, the feeling of that part is rendered uncommonly acute. Even infenfible parts, as tendons and bones, from difease become extremely fenfible. In fhort, wherever there is an increase of vascular action in any part of the body, it is always attended with a proportional increase of fenfibility.

This opinion, which stands opposed to the doctrine of 3 A 2

tenfion,

tenfion, is greatly ftrengthened by an experiment related by Dr. Beddoes. He made a blifter on his hand, and cutting it in fixed air, which holds too firmly its oxygen to difengage it, he experienced no fenfation of pain; he then exposed his hand to common air, when he immediately felt pain, and afterwards to oxygen air, when the pain became intense; then removing it to the fixed air, he felt an almost instantaneous relief.

It has been obferved, moreover, that the animation of those who inhale a super-oxygenated atmosphere is greatly increased, whereas in diseases where there is a defect of this principle in the conftitution there is the greatest ennuie.

The power of wine in raising the fpirits, is fuppofed to arife from the fame caufe, viz. by increafing the attraction of the blood for the vital or oxygenous portion of the air, as was before obferved, when relating the experience of the celebrated diver Mr. Spalding *.

* Vide page 89.

SECT.

SECT. XXXV.

LAW II.

A TOO GREAT EXCITEMENT OF ANY ORGAN EXHAUSTS

THE EXCITABILITY OF THE CONTRACTILE FIBRE.

1. Of exhaufted Irritability.

EVERY ftimulus which affects one of the fibres affects the others at the fame time, and in like manner. Hence "the fympathy of different and separate parts, and those furprising phænomena which hitherto have been explained by the harmony of the nerves. These sympathetic phænomena are obfervable throughout all organized nature. Whatever part of the polypus be touched, the whole will contract, and its arms will contract themfelves by fympathy. If a worm be touched with the point of a pin, without wounding it, the whole worm will be feen to contract itself; which is a certain proof that the different parts are affected by fympathy. Hence the irritable fibres, which are combined together in every individual, whether animal or vegetable, form A SYSTEM OF FIBRES, in which the integral parts act con

tinually

tinually upon the whole, while the whole re-acts upon the parts, fo that every ftimulus which acts upon any fibre in the system, will deprive that part of its irritability; but this lofs will be foon repaired by the fyftem, and every fibre will furnish in proportion fome fhare of its own irritability to fupply the loss in any one fibre. Thus it is that a too powerful fiimulus acting upon any one part of the fystem, such as the abuse of spirituous liquors, and tonic medicines, exhaufts in the end the whole fyftem, and produces death. For the fame reason, a very powerful stimulus applied to one part of the system, fuch as the poifon of a rattlefnake, will, in an inftant, exhauft all the irritability, render the blood fluid, and destroy the animal.

From what has been faid, it will appear, that the IRRITABILITY of the system is never in a permanent condition, but inceffantly ebbing and flowing like the tide; constantly in motion, like the pendulum in its vibrations, or rather bearing resemblance to the Leyden phial, when it is alternately charging, difcharging, and difcharged.

When the fum of the ftimuli acting upon the contractile fibre is too great, the fibre lofes more irritability than it receives, and of courfe in a fhort time finds it

felf

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