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SECT. XXXIII.

OF THE VITALITY OF THE BLOOD.

THE vitality of the blood was a doctrine first broached by the immortal HARVEY. This, like the circulation, was paid however little attention to, until it was revived by the illuftrious JOHN HUNTER.

This idea led to a very important discovery in natural philosophy, namely, that it is to the atmosphere, and to that particular part of it which goes by the name of vital, or oxygen air, that we are indebted for that vitality which is communicated to the blood, and which animates our bodies, and is the immediate bond of union betwixt our immaterial foul and this vifible world.

The blood, fays the immortal HUNTER, has as much the materia vitæ in it, as the folids, which keeps up the harmony that exifts between them. And as every part endued with this vital principle has a fympathetic affection from appofition of parts, as to affect each other; fo the blood, and the body, are capable of affecting, and being affected by each other. The blood being evidently compofed of the fame conftituent principles as the body,

and

and being endowed with the fame living powers as the contractile living fibre; and as having evidently no communication with the brain, it affords one of the ftrongest proofs of the vital principle in both folids and fluids, being independent of the nerves; and is fimilar in this respect to those inferior order of animals and plants that have no nerves, but where the living principle is diffufed throughout the whole.

Refpirable air, fays this eminent anatomift, has the property of heightening the red colour of the blood to a fearlet, and this, with its confequent heat, is fuppofed to be the chief or only use of respiration:—but if we suppose the change of colour in the red globules to be all that respiration is to perform, we shall make the red globules the moft effential part of the blood, whereas that may be faid to be the leaft. It is most probable, that the effect of air on the blood is greatest on the coagulable lymph; and this conjecture is rendered more likely, when we confider, that in cold animals * which have no red globules, reSpiration

* Having at hand fome water from the hot-well at Bristol, which I had found to contain air in a state of great purity, I completely filled, says Dr. PRIESTLEY, a large phial of it, and I put into it a few very fmall fish, which I had provided for the purpose of thefe experiments. They were min

nows

fpiration is as effential to their existence as in any

other.

Coagulation, Mr. Hunter conceives to be an operation of life fimilar to muscular contraction. The coagulability of animated fluids will be found fubject to the fame laws as the irritability of the fibre. This is a new difcovery; and it forms the bafis of many important truths.

A piece, three inches in length, being cut out from a ftraight muscle in an ox's neck, immediately after his being knocked down, was placed in a freezing mixture for fourteen minutes. At the end of this time it was only two inches in length. Upon being thawed gradu

nows, and other small fish about two inches in length. In this water they were confined without any access of common air till they died.

After this I took equal quantities of the water in which the fish had died, and of that out of which it had been taken, where they were confined in; and I expelled from both all the air which they would yield. That from the water in which no fish had been put, exceeded in quantity that from the water in which they had been confined, in the proportion of 3 to 2; and examining the quality of both these quantities of air, by the test of nitrous air, the former exceeded the latter in a still greater proportion.

The air from the water in which no fish had been confined was at the ftandard of common air, but that which had been contaminated by the respiration, as I may fay, of the fith, was fomething worse than air in which a candle juft goes out.

From this experiment it may be concluded with certainty, that air contained in water, in an unelastic state, is as neceffary to the life of fish, as air in an elastic ftate is to that of land animals.

ally,

ally, in about fix hours after thawing, it contracted fo as to measure only one inch. Here then were the pieces of muscles frozen, fo as to prevent all power of contraction in their fibres, without destroying their life; when thawed, they fhewed the fame irritability, which they had before; this is exactly fimilar to the freezing of blood too faft for its coagulation; which, when thawed, does afterwards coagulate, as it depends in each on the irritability of the part not being destroyed.

As the heat of 120 degrees excites the blood to coagulate, he wished to try how far mufcular contraction was fimilar in this refpect. He took a piece of a muscle from a fheep newly killed, and put it into water heated to 120 degrees, when it contracted directly, fo as to become hard and stiff.

Animals killed by lightning, and also by electricity; have not their muscles contracted: this arifes from the irritable principle being instantaneously destroyed in the muscles, which therefore cannot be affected by any ftimulus, not even the pain of death. In fuch cases the blood does not coagulate. Blows on the ftomach kill immediately; and the muscles do not contract, nor does the blood coagulate. Death from fudden gufts of paffion

is of this kind; and in all these cafes the body foon putrefies after death. Animals that are run very hard, and killed in such a state, or, which produces a ftill greater effect, are run to death, have neither their muscles contracted, nor their blood coagulated: and in both cafes the effect must be in exact proportion to the cause.

In the West India iflands they kill their poultry with vegetable poisons, in order to render them tender without keeping. For the faine reason, the expedient was devised to fatisfy a fhameful gluttony, namely, the flogging of animals to death.

The general debility, and laxity of the mufcles, brought after repeated venefection, and the great proftration of ftrength, and even death, produced by hæmorrhage, when the evacuation of the blood is confiderable and suddenly made, must be confidered as a ftrong proof, added to the thin ftate of the blood, of the living principle being inherent in the blood, and of its having a fimilar nature as the muscular fibres.

On the contrary, in difeafes where the action of the heart was going on very strong, the mufcles after death contract ftrongly, and the blood strongly coagulates. This coincidence of coagulability in the fluids, and irritability in the folids, that is, both shortening their 3 A dimenfions,

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