3d. An increased amount of blood is determined to the brain, and wakefulness is produced by certain substances used as food or medicine.
Daily experience assures us of the truth of this proposition. In general terms, it may be said that all those substances which, when ingested into the system, increase the force and frequency of the heart’s action, cause also a hyperæmic condition of the brain and tend to the supervention of wakefulness.
Chief among these agents are to be placed alcohol, opium, belladonna, stramonium, Indian hemp, tea, and coffee. It is true that the first two of these, when taken in large quantities, sometimes give rise to a comatose condition. This, however, as has already been shown, is not a consequence of an increased amount of blood in the brain, but results from the circulation in that organ of blood which has not been duly oxygenated by respiration. My experiments on this head have been many, and show conclusively that neither alcohol nor opium possesses any stupefying effect, if means be taken to insure the full aeration of the blood. If, however, these substances be administered beyond a certain limit, they so act upon the nerves which supply the respiratory muscles as to interfere with the process of respiration, and hence the blood is not sufficiently subjected to the action of the atmosphere. Unaerated blood therefore circulates in the brain, and coma—not sleep—is produced.
No substance is capable of acting as a direct hypnotic, except that which lessens the amount of blood in the brain. In small doses alcohol and opium do this indirectly, through their stimulating properties exerted upon overdistended blood-vessels, as has been shown in regard to the first named in a case already cited; but they never so act upon the healthy brain. In the normal state of this organ their action in small doses is always that of excitants. The word “small” is of course used in a relative sense. What is a small dose for one person may be a large one for another, and vice versa.
In this connection it is scarcely necessary to dwell at any length upon the wakefulness produced by delirium tremens from the excessive ingestion of alcohol or opium. In the post-mortem examinations—four only—which I have made of individuals dying from this affection as the result of the immediate use of alcohol, the brain was invariably found congested. Either hyperæmia or its consequence, effusion of serum, is the ordinary pathological condition discovered in such cases.
In regard to opium, most practitioners have doubtless noticed the effect which it and its preparations frequently produce in preventing sleep. I have known one dose of half a grain of opium keep a patient awake for three consecutive days and nights, during the whole of which period intense mental excitement was present. As is well known, the Malays, when they wish to run amuck, bring on the necessary degree of cerebral stimulation by the use of opium. During the condition thus produced insomnia is always present. It is certainly true, however, that in moderately large doses opium acts as a direct hypnotic, and the same may be said of other narcotics.
Belladonna, stramonium, and Indian hemp likewise produce congestion of the brain and wakefulness. The latter, under the name of hashish,[137] is still used in the East to bring on a state of delirium, and, if rumor is to be credited, has its votaries in this country. Tea and coffee act in a similar but far less powerful manner. As one of the results of experiments with these substances, instituted upon myself, I found that the circulation of the blood was rendered more active.[138] Their influence in preventing sleep is well known to the generality of people, and this effect is doubtless entirely due to their action upon the heart and blood-vessels by which the amount of blood in the brain is increased. In persons of fair and thin skins, who are not accustomed to the use of either of these beverages, the face can be seen to flush after they have been taken; and I have frequently met with persons in whom their use was always followed by suffusion of the eyes, and a feeling of fullness within the head. Their power to increase the force and brilliancy of our thoughts, and to sustain the mind under depressing influences, has long been recognized, and is to be ascribed to the same cause as that which prevents sleep.
4th. Wakefulness is also caused by functional derangements of certain organs of the body, whereby an increase in the amount of blood in the brain is produced.