Facts analogous to those observed in animals have been studied directly in the human brain. Upon a person injured by a frightful railroad accident the effect of a considerable loss of brain-substance was examined. The brain was visible over a surface of three by six inches. The patient suffered frequent and severe attacks of epilepsy and coma, during which the brain invariably expanded. Sleep succeeded these attacks, and the cerebral hernia gradually subsided. When the patient awoke, the brain again projected and rose to the level of the surface of the external, bony table. In the case of another person injured in consequence of a fracture of the skull, the cerebral circulation was studied during the administration of anaesthetics. With the first inhalations, the surface of the brain became branchy and filled with blood; the flow of blood and throbbing of the brain increased, and then, at the instant of sleep, its surface subsided by degrees below the opening, while at the same time growing relatively pale and bloodless.
Briefly, then, the brain is governed by the common law that controls blood-circulation in all the organs. By virtue of this law, when the organs are at rest and their action suspended, the circulation in them grows languid; and it increases, on the contrary, as soon as activity is resumed. The brain, I repeat, is no exception to this general law, as had been supposed, for it is now demonstrated that the state of sleep coincides not with congestion, but, on the contrary, with bloodlessness of the brain.
If we seek now to understand the relations that may exist between great activity of blood-circulation and the functional condition of the organs, we shall readily see that this increased flow of the sanguineous fluid corresponds with greater intensity in the chemical alterations going on within the tissues, as also with an exaltation in the phenomena connected with heat which are their necessary and immediate consequence. The production of heat in living beings is a fact established from remote antiquity; but the ancients had erroneous ideas as to the origin of heat: they attributed it to an innate organic power that had its seat in the heart, that ardent centre of ebullition for the blood and the passions. At a later date the lungs were regarded as a sort of furnace to which the mass of the blood repaired successively to gain the heat which circulation was bidden to distribute throughout the body. The advance of modern physiology has proved that all these absolute consignments of vital conditions to special points are chimeras. The sources of animal warmth exist everywhere, and in no region exclusively. It is only through the harmonious functional play of the various organs that the temperature is kept nearly constant in man and the warm-blooded animals. There are, in truth, as many heat-producing centres as there are special organs and tissues, and we are obliged always to connect evolving heat with functional labor of the organs. When a muscle contracts, when a mucous surface or a gland