Page:Popular Science Monthly Volume 2.djvu/710

690 circulation was so entirely successful that the veins on the back of the hand presented a bluish tinge; a heating like that of the pulse lifted the main artery of the wrist, muscular life revived; the fingers soon lost their stiffness, and at forty-five minutes after eleven irritability had reappeared in the muscles of the arm; it was still perceptible at four in the morning of the next day.

Experiment has never more clearly proved that the blood is essential to muscular life. In the limbs of these subjects the organic matter was decomposed, and all vital manifestation had become impossible. A flow of blood throughout them was effected, and at once this muscular flesh becomes contractile again; the special activity of the motor fibre is reanimated, and its functions performed as in life. It will, of course, be objected that the muscular element receives its conditions of activity from the motor nerves, and that the blood-globules only vivified it indirectly, by restoring excitability to the nerves; but has not the mode of action of curare proved that the life of the muscle persisted after the physiological death of the nerve? If the arteries of the lower limbs of a living animal are tightened by a compress, the withdrawal of the blood will in the same way cause the properties of the nerves to disappear before those of the muscles; an artificial stimulus, directly applied to the muscular fibre, will still produce movement, after nervous excitability has ceased to exist. If you then remove the compress, you set the flow of the blood free, and the peculiar action of the motor nerves is completely restored. Thus the life of the nervous element itself has been successively extinguished and revived; after that the inciting stimulus from the train of the spinal marrow may be transmitted through the medium of this conductor, which possesses a real autonomy.

The nerves of general sensation, like the nerves of motion, demand the contact of arterial blood. The anatomical distribution of these nerve-elements does not allow the action of the sanguine fluid upon them to be studied as to their surfaces; yet sensation constitutes too well-defined a function not to be the object of experimental analysis, as motion is; this analysis is made by the help of transfusion upon the spinal marrow, the organ that receives all impressions made on the skin. Physiologists have used an ingenious process to prevent the blood from moistening this nervous centre: they inject a liquid filled with an inert powder into the vessels, in a uniform direction; the capillary parts of the circulation are soon clogged, the spinal marrow ceases to be in relations with the blood, and ceases at once to receive impressions from the skin. The same phenomenon is observed when all the blood-vessels that go from the main artery of the body to this nervous centre are artificially destroyed; the return of sensation takes place only when arterial blood is restored to the spinal cord. This fact is also proved by the transfusion of new blood into the veins of an animal that has yielded to a hæmorrhage. Again,