My friend, Professor Foà, showed in a work carried out together with Professor M. Schiff,[14] that even when heart and blood-vessels no longer respond, when the circulation is no longer modified, whatever may be the perturbation of the nerve-centres, a last trace of sensibility may still be observed in the eye, the pupil dilating whenever the animal is irritated. [14] Foà e M. Schiff. _La pupilla come estesiometro._ In the _Imparziale_, 1874, p. 617. But I have seen dogs, poisoned with chloral, of which the temperature had sunk to 30°, so extremely slow had the chemical processes of respiration become; no electric current, no mechanical action was capable of producing even the slightest movement of the limbs or face; the pulse, pressure of blood, the pupil, in a word everything had become impassive, no effect being obtained on the pulse even when the cardiac nerves were laid bare, severed, irritated by electric currents--and yet the animal was still sensible. By carefully studying the respiration I saw that it was modified whenever a leg or any other part of the body was pinched. The alteration of the breathing is therefore the last function of the organism in which sensibility and emotion reveal themselves. V We know that, whatever nerve of the skin is irritated, a succession of deeper and more frequent inspirations follows, and we have seen that this phenomenon is useful to the organism. But if the excitement of a nerve becomes so strong as to cause violent pain, or if a very vivid impression is received as in fright, the mechanism stops short midway in a deep inspiration, and this is injurious. Some few times I have been in danger of my life, and always remember to have felt a terrible oppression, as though my breath had been cut short. A few months ago I was overtaken by a storm on the mountains, when the lightning struck the ground about fifty steps from me, and I remember having noticed that respiration was arrested for several seconds. We, who carry this fragile machine of our body about with us continually, ought to remember that every shock which exceeds the usual measure may prove fatal. A slight touch of the pendulum accelerates the rotation of the wheels, a stronger one stops their movement; a slight impetus helps us onward, a rude push throws us to the ground. It is thus that the phenomena of fear, which may be useful to us in lesser degrees, become morbid and fatal to the organism as soon as they exceed a certain limit; for this reason fear must be looked upon as a disease.