Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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withstanding, a pressure of the brain there certainly is. The surface of the brain, seen through the circular opening made in the hone, is observed to pulsate — and to pulsate with a twofold motion. With every systole of the heart, the brain-surface pro- trudes a little, and it again subsides with the succeeding diastole. This shows that the tension of the arteries, produced by the given contractions of the ventricles of the heart, exerts a degree of pressure upon the contents of the cranium. In the second place, the brain has also an alternate move- ment, corresponding with the movements of the thorax in breathings, — rising- with every act of expiration, and sinking with every act of inspiration. This I have demonstrated. Now, during expiration, the blood escapes less freely from the head through the veins; and thus again vascular fulness is found connected with evidence of pressure on the contents of the bony dome. When we reflect that more blood may be forced through the arteries into the brain than the venous capillaries readily transmit and thus remove again, it is easy to conceive of varying- pressure upon the nervous mass within the skull, which may arise from plethora, blood poison, or deficient nerve power. This may arise also, on the other hand, from a reverse state of tilings, i. e., where there is too little blood, or " poor blood," etc.; for then the venous capillaries take it away too readily, — i.e., more readily than the arteries supply it, — and there must be insufficient pressure, as well as a want of brain nourishment. In point of fact, we know of some changes in the circulation through the brain, which have the effect, invariably, first, of modifying, and, at length, — if they are con- tinued,— of arresting the cerebral functions. If no blood, or if impoverished blood, be sent through the arteries to the brain, death, in the way of syncope, ensues ; if venous blood, or blood poisoned with bile, or uric acid, circulates in those brain blood vessels, it leads to death by coma. But, whatever be the nature of the unknown, and, perhaps, fugitive physical conditions of the nervous centres thus capable of disturbing, or even abolish- ing, their functions, it is useful to keep in our minds a distinct and clear conception of the fact, that there must be some such