III
Let us now see of what parts the respiratory machine consists, and how it puts its force into operation. In man the different parts of this mechanism never act sufficiently in independence of each other to allow of our surprising them separately at work. Only after decapitation has the head been seen to make inspiratory movements although separated from the trunk. Physicians who have had to be present at the execution of the condemned tell of the terrible effect produced when the head of the man rolls, gasping, to the ground, becoming instantaneously of a corpse-like pallor, and disfigured by strange, spasmodic contractions, the eyes rolling irregularly, horribly, for several seconds. The trunk is already motionless, the blood, which at first poured forth in great streams from the arteries of the neck, only spurts feebly and at intervals, still obeying the weakening pulsations of the heart. The eyes at last turn upwards, but life is not yet quite extinct, the mouth still opens from time to time as though with a great effort. The inspirations which at first distended the nostrils and opened wide the mouth soon become less distinct and less frequent, until at last they die away altogether.
If, after cutting off the head of a very young animal, we stop the hæmorrhage by means of a bandage and then introduce a bellows into the trachea, so that respiration may be artificially stimulated, we see that the headless animal begins to breathe after the cessation of the perturbing influence of the first shock. With kittens it is sufficient to administer a small dose of strychnine (0·0005 gr.) in order to produce respiratory movements in the trunk after decapitation, which, however, become gradually weaker as they no longer suffice to maintain the excitability of the nerve-centres through the oxidation of the blood.
This simple experiment proves that respiration is accomplished by nerves branching off from the brain and spinal cord. The consciousness of our ego is not necessary; even a decapitated animal responds by modifications of respiration when we pinch or squeeze his paws, because the sensory nerves of the skin transmit the impressions of the external world to the spinal cord. The deep, noisy, and interrupted inspirations of anyone taking a plunge-bath are also involuntary, and when we are overcome by fear it is the same mechanism which produces a deep inspiration.
At every step which physiology makes, we discover fresh complications, other wheels, if I may use the expression, within the wheels of our organism. Until quite recently it was thought that the brain controlled the respiratory centre, accelerating or arresting its movements; but it has now been shown by Christiani that by means of a vivid light which must strike the eyes of the animal, deep and frequent inspirations may be produced even after the brain has been removed. Impressions of sound, which would have frightened the animal, produce the same effect, the oppression being even greater than in normal conditions. This experiment shows us that, independently of cerebral action and psychic operations, the rhythm of breathing alters at every change which takes place in the external world, at every peripheral irritation of the sensory nerves. Thus are explained the oppression and palpitation of the heart which befall us at the banging of a door, at a clap of thunder, and which we cannot suppress, which are produced by a sudden noise on a thousand occasions before we learn the cause, and do not disappear even when we have done so, and recognised the unimportant origin of our perturbation.
In these studies, also, the materiality of psychic processes becomes evident, as well as the slowness of operation in those phenomena which are believed to be the most rapid in life.
Just as an electric spark or a flash of lightning which lasts the one-thousandth part of a second leaves an impression in us a hundred times longer; just as our eye is unable to follow the different positions of a burning brand swung round in the dark, but sees, as it were, a ribbon of fire; just as we burn our hand when we touch a glowing object before we have time to feel the pain; just as, when in movement, we often stumble against obstacles which confront us without our having time to stop; so the impressions which reach the nerve-centres keep us agitated for some time without our having the force to stand still midway on the declivity down which the sudden impetus of the emotion is speeding us. We have all experienced this inability of the organism, we know that we do not succeed in subduing even the slightest mental perturbations. Suppose a person is walking quietly along, when suddenly he sees before him the figure of a man whom he was trying to avoid. At once his blood begins to boil. Scarcely, however, has he seen the man before he becomes aware that he has made a mistake, and he is glad; but his heart has already begun to beat more vigorously, the perturbation and oppression do not at once subside, but continue to annoy for some time. They are like the continued vibrations of a cord that has been shaken, like a flame shooting up as the spark disturbs the equilibrium of the molecules in the nerve-centres, like the echo of a sound reverberating in the nervous fibres and slowly dying away.