SECT. VII.

ON EXERCISE.

THIS fubject has been already confidered in a philofophic point of view in Sect. XII. page 126.

It was there fhewn, that when muscular intumefcence took place, certain chemical combinations were formed, productive of the VITAL FLAME.

If I walk flowly along, for the space of a quarter of a mile upon even ground, my breathing and pulse are but little accelerated, and the heat of my body remains nearly the faine as before. But if I walk at the fame расе, and for the fame distance, up a steep hill, or bearing a heavy burthen, my breathing becomes Short and full, and my heart beats firong and quick, and the heat thrown off from my body correfponds with thefe increased internal move

ments.

It is natural to afk, what is the cause of this difference, when the pace, the Speed, and the actual movement of the mufcles are the fame? It certainly arifes from the quantity of nervous electricity tranfmitted from the BRAIN to the muscles in the latter cafe, where the body was

raised on high, or where a weight was carried, being much greater than when the body is only moved, without being lifted up, or without any additional weight upon it. For though the motion of the muscles be the fame in both cafes, yet the increased weight to be moved, required the nervous exertion to be much greater in the latter inftance than in the former; and therefore the will, or determination of the mind, propelled a greater quantity of nervous electricity, from the BRAIN to the muscles employed.

To the increafed demand on the fyftem of OXYGEN AIR, to be decompofed by the nervous electricity*, the accelerated refpiration must be attributed; and from the increased quantity of OXYGEN AIR in the blood, we can account for the improved digeftion †, and a more rapid circulation; and from all these causes, concurring with the electricity of the nerves, we are able to fee clearly the reason of the increase of the vital flame.

*The oxygen air thus procured to the blood from the want of the system, is faid to proceed from the vis medicatrix naturæ, and by others from association or Sympathy. Thus the call of the ftomach for food after a fever does not arife from the stimulus of the gastric juice, but from the want of the system. Thus a ftimulus on the faciderian membrane of the nofe occafions Sneezing, &c. &c.

+ Vide Sect. VIII. on the Balance betwixt Refpiration and Digeftion.

Obfervation

Obfervation 1. If an animal, a man, for instance, in good health, be expofed to a temperate air, in a state of reft, the quantity of vital heat, generated by the continued attractions of OXYGEN going on in the body, will be fufficient, with a certain quantity of clothing, for maintaining the temperature of about 97 degrees, by which the folids receive their natural stimulus, the fluids retain their proper fluidity, and all the functions of life are duly performed, and a fufficient quantity abounds to carry off the perfpirable fluid.

Obfervation 2. If a man, exposed to a frofty air, continues at reft, the principles in his body attractive of OXYGEN, cannot generate a fufficient quantity of vital heat to keep every part of the body at its right temperature; because the coldness of the furrounding medium carries off the heat fafter than they can produce it; confequently the folids and fluids of the extremities, and at the furface of the body, will become frigid, and the fibres torpid, and the death of the extreme, and laftly of the vital parts, enfue.

Obfervation 3. But, on the contrary, when a man exposed to a frosty air, perceives the coldness, and torpor, arifing from his body being deprived of its heat, faster than the principles in his body attractive of OXYGEN

can furnish it; if he throws the voluntary muscles into action, the quantity of heat generated by the nervous electricity, will be fufficient to warm every part, and recover and maintain the natural temperature; although the air fhall ftill continue to withdraw rapidly the vital heat from the furface of the body.

Some very pleasing experiments are related by Dr. PEART (whofe name would be oftener mentioned with fill higher refpect, were we fortunate enough to rank him among the many illuftrious converts to the new chemistry), which prove that partial exercife conveys a glow over the whole body..

1. EXPERIMENT.

I put my hand, fays he, firft into cold water at 56 degrees of temperature. After fifteen minutes I withdrew it, and found the temperature of the water raised to 65,

It had gained therefore, in fifteen minutes, 9 degrees

of heat.

2. EXPERIMENT.

The fame day I put my hand as before, but instead of keeping it, and my body, in a state of perfect reft, I

threw many of the voluntary mufcles into action, and in fifteen minutes the water at 56 degrees was raifed

to 73.

Here it had gained 17 degrees of heat.

3. EXPERIMENT.

To prove that the exertion of any fet of muscles affects the quantity of heat generated within, and thrown off from the whole body, I introduced my hand into the fame quantity of water, and at the fame temperature as in the first experiment, and I pushed my feet against a large book-case, firmly fixed by its own weight, and my arms were forcibly stretched out. By the exertion of these few muscles only, without any motion of the fibres, fo much of the electric fluid was tranfmitted to these parts, and so much heat difengaged that its ftimulus extended over the whole body, and the water in fifteen minutes rose in confequence to 14 degrees, that is, five degrees more than where the body was in a state of perfect reft t.

Dr. PEART has the nervous fluid.

*

The fame is proved, though not quite fo philofophically, by the vulgar mode of warming the body by throwing the arms across, or by the more elegant, but partial, exercise of what are called dumb bells.

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