III
Let us enter more fully into this subject, so that we may understand the meaning of certain phenomena accompanying fear.
The materials rendered useless in the operations of our factory are easily eliminated through the skin, which thus co-operates in one of the most important functions, that of internal cleansing, which is more particularly the office of the kidneys.
We have all observed that we usually perspire when the skin is red; but there are exceptional cases, as in fear, when we perspire, although we are pale and trembling. How does it happen that we have a cold perspiration, and a perspiration with a sensation of warmth in the skin? I shall here mention an experiment of Claude Bernard. Having severed a filament of the sympathetic nerves on the neck of a horse, he saw immediately afterwards, although the animal had not moved, an abundant secretion on that half of its head where the cut had been made. The mechanism producing this phenomenon is easily understood: as soon as the nerve is severed which held the blood-vessels in check, the latter dilate, blood flows more copiously to the sudoriparous glands, increasing their activity and causing an elimination of the secreted liquid.
When it is warm, or when we are feverish, and the blood tends to flow more abundantly to the surface of the body to cool itself, the secretion of perspiration is increased in a similar way. But we see anæmic persons perspire—the consumptive, for instance, and the dying, in whom this more copious supply of blood is wanting. In this case the cause of abundant secretion is different; here it is the nerves. One of the finest discoveries which have been made of late years in physiology, is that of the nerve-filaments which connect the cerebro-spinal system with the glands of the body. Whereas formerly everything was attributed to the more or less copious flow of blood to the glands, the secretions of which were considered as a process of filtration, we now know that the matter is much more complicated, and that there are nerves which augment and diminish the activity of the cells charged with the secretion. It is nervous activity which produces the perspiration characteristic of attention, pain, epilepsy, tetanus.
In order to prove that the secretion of perspiration may be accomplished independently of the circulation of the blood, we make an incision in the leg of a cat immediately after death and irritate the sciatic nerve; we then see that a secretion of perspiration still appears on the sole of the foot. From this we can understand how in the death-agony and the extreme pallor of fright, when all the vessels of the skin are contracted, there yet may appear a peculiar secretion of perspiration which we call cold perspiration.
IV
There is another part of the body which opens periodically to allow of the ejection of the refuse of the factory; it consists in a cloaca and a cistern which contains a yellow liquid. It is a less beautiful part of the organism, but during violent emotions involuntary movements are produced in it so characteristic of fear that we must turn our attention to it. Physicians thought that these irregularities were caused by a paralysis of the sphincter muscle, but this is not the case. The researches which I made with Prof. Pellicani[26] showed that, in man as well as in animals, there are strong contractions of the bladder which correspond to psychic facts. Scarcely have we experienced some slight emotion or been excited by some thought but there is an immediate change in the state of the muscles of this organ. I regret that the nature of this book does not permit of the reproduction of the curves traced by the plethysmograph, which show that psychic phenomena and any irritation of the sensory nerves produce a contraction of the bladder.
This is the reason why, during emotion, we feel the urgent and repeated need to expel the urine, without the amount of accumulated liquid being such as to explain the necessity. We can no doubt all remember the annoyance which the contraction of this organ caused us on certain solemn occasions; for instance, when we had to make a speech, or present ourselves for an examination, or were anxiously expecting something.
The feeling of contraction and pressure in the abdomen when we approach a precipice, or when we are in great apprehension, is solely due to the involuntary contraction of the bladder. We have shown that all causes producing a contraction of the blood-vessels have the same effect on the muscles of the bladder. I have often seen excitable, good-tempered dogs, in whom caresses and the sight of food were sufficient to produce such a contraction of the bladder, that the urine was expelled; and this suffices to confirm the fact that in our organism the same phenomena may be produced by opposite causes.