8 Centralblatt f. d. Med. Wiss., 1871, p. 706.
9 Centralblatt f. d. Med. Wiss., 1878, p. 454.
Several cases are reported by P. R. Hoy10 where pressure upon the brain produced an arrest of function, which was resumed when the pressure was removed. In the first of these a piece of bone had been removed, but the dura was intact. If the patient were asked a question and the finger immediately pressed upon the dura, no answer was made, but as soon as the finger was removed the reply came. In two other cases, which are not without their parallels, the patients resumed after trephining the mental attitude in which they had been surprised by the injury—in one case hours, and in the other years, before.
10 Journ. Nerv. and Ment. Dis., vol. iv. p. 288.
The natural generalization to be made from these cases and experiments is, that pressure upon the brain-tissue suspends, for the time, its function; but when we find exactly the same symptoms arising from either sudden or gradual occlusion of the vessels where we can hardly imagine increased pressure to exist, except perhaps over a very small area of collateral hyperæmia, we must go a step farther for a common factor; and it seems possible to find one which will not only explain the several conditions spoken of, but also others which closely resemble them. Simple anæmia will cover the cases of hemorrhage and embolism, but certainly not narcotic poisoning and certain other conditions where characteristic apoplectic symptoms exist without discoverable lesion. If, however, we say that a deprivation of a considerable portion of gray matter of its due supply of arterialized and healthy blood suspends for a time its functional activity, we can explain the similarity of results arising from very different causes.
In a case of cerebral hemorrhage of considerable size the pressure is distributed over a space much exceeding the area of the clot itself, and renders a large part of at least one hemisphere anæmic. If the blood finds its way into the ventricles, the conditions are most favorable for compressing nearly the whole brain. The anæmic appearance of the cerebral surface is often remarked at autopsies.
When an embolus lodges in an artery and produces complete occlusion, the portion of brain supplied thereby becomes at once entirely anæmic, since the arteries on the surface have so slight anastomoses that they are entirely unable to supply the deficiency, except to a slight extent around the edges of the vascular territory involved. The anæmia, however, does not extend beyond the territory originally affected, and consequently we may have extensive paralysis from embolism without a marked apoplectic attack. In extreme congestion of the brain the reverse may seem to be the case.
In reality, the hindrance to the proper functions is nearly the same, since blood which is not duly renovated and contains the products of metamorphosis of tissue in excess is worth as little for healthy nutrition as no blood at all. There is no reason to suppose that blood in circulation, no matter in how great quantity, gives rise to unconsciousness. It may cause over-action or disordered action, as in mania, but not arrest of action.
The narcotic poisons also deprive the nerve-tissue of its healthy food; whether by interference with oxygenation and depuration, or by a direct action of the substance itself on the nerve-cells, it is not easy to say. The fact that the completeness and duration of the unconsciousness are not in proportion to the paralysis or anæsthesia shows that they are to some extent independent of each other; and, although it is possible to locate with some precision the lesion which abolishes motor power and conscious sensation, yet we cannot say how much or what part of the brain must be deprived of its function in order to produce that cutting off of all conscious relation with the external world and reduction of a feeling, thinking, remembering, and acting organism to the level of a mere automatic breathing-machine, which we designate as loss of consciousness.
In fact, in the present state of our knowledge as to what consciousness is, any speculation as to its seat would be a waste of time, and we must content ourselves with recognizing that experience seems to show that a large part, rather than any particular part of the brain, must be involved, not necessarily in the primary lesion, but in the resulting pressure or anæmia.