In joy and intense pain there is a degree of emotion in which the intonation of the voice is changed, because the nerves which move the muscles of the larynx no longer regularly adjust the vocal cords. This is the origin of the tremolo which serves to heighten the pathetic expression in singing. Many are scarcely able to speak, but stammer under the influence of an emotion. It is difficult to pitch a loud note and sustain it with expanded chest without the voice trembling; in the same way one cannot scream for any length of time without the voice turning shrill and harsh, because the muscles tire and the movements of the larynx can only be imperfectly regulated; similarly, when we write after running or violent exercise, certain unusual flourishes appear which make the characters unrecognisable.
I have noticed a curious tremor during inspiration in suffering men and animals. I have found it in a less degree also in healthy animals, particularly in dogs. At every inspiration there is a very noticeable tremor of the limbs and of nearly the whole muscular system. The excitement arising in the nerve-centres to produce a contraction of the diaphragm and of the muscles of the thorax seems to have become so strong, that it goes beyond the limits of the respiratory centre and diffuses itself over a great part of the nerves. In anger, fear, and mental perturbations, when the stormy winds of passion rage, waves flow to all parts of the nervous system, then break, revealing themselves in the agitation of the muscles.
Trembling often has a peripheral origin, and may be due to both heat and cold. It is sufficient to hold the arm in water heated up to 48° or 50° in order to produce a visible tremor. This fact, which I observed repeatedly on my brother, corresponds to the chattering of the teeth when a cold stream of air strikes our face.
V
Very excitable dogs often tremble when another dog approaches. I know one that trembles like a leaf whenever, from the height of a second floor, he sees a bigger dog passing in the street. This lively alarm is quite pitiable, and after all most unnecessary, for the most of his supposed rivals do not perceive his presence, nor even look up. But as soon as he catches sight of them in the distance, he becomes suspicious, a feverish shiver goes over him, the hair on his back stands on end, his whole body trembles, while he cowers near the window with ears erect, looking fiercely out of the corners of his eyes, snarling, and showing his teeth—a ridiculous instance of timid arrogance and despised pride.
But most clearly does trembling become manifest during fear. As army surgeon, I had once to be present at the execution of some brigands. It was a summary judgment. A major of the bersaglieri put a few questions to one or two, then turning to the captain said simply: 'Shoot them.’ Some were dumb-founded and stood open-mouthed, petrified; others seemed indifferent. I remember one lad, of scarcely twenty years of age, who mumbled replies to a few questions, then remained silent, in the position of a man warding off a fatal blow, with lifted arms, extended palms, the neck drawn between the shoulders, the head held sideways, the body bent and drawn backwards. When he heard the dreadful word, he emitted a shrill, heart-rending cry of despair, looked around him, as though eagerly seeking something, then turned to flee and rushed with outspread arms against a wall of the court, writhing, and scratching it as though trying to force an entrance between the stones, like a polype clinging to a rock. After a few screams and contortions, he suddenly sank to the ground, powerless and helpless, like a log. He was pale and trembled as I have never seen anyone tremble since; it seemed as though the muscles had been turned to a jelly which was shaken in all directions.
Even in their minor degrees apprehension and fear make us tremble. When hurried one cannot perform any minute work, the convulsive fingers can grasp nothing. I know timid girls who are ashamed of the trembling of their hands when filling the tea-cups of their guests.
A gentleman in Germany told me some very curious things about his excitability, amongst others that he had had to give up dancing, as his legs left him in the lurch at the least emotion. Everything disturbed his equanimity; if he had to offer his arm to a lady to take her in to dinner, or to walk across the room when in company, the mere thought of being observed made him tremble and totter as though intoxicated.
The kneeling attitude which one finds amongst all people as a sign of adoration, love, and as the position of one imploring pardon or mercy, must be ascribed to the physiological fact that strong emotions cause a sudden trembling of the legs and oblige us to sink to the ground.