Every agreeable impression produces an increase in the volume of the arm and in the height of the pulse, with increased depth of the respiratory cavity. A disagreeable impression, when weak, immediately produces a diminution in the volume of the arm and the height of the pulse; but almost at once the volume begins to increase, notwithstanding the diminished pulse, and usually passes beyond its normal state, even when the pulse has returned to its first condition. If the impression is strong but not painful these changes are accentuated, and from the first are accompanied by deep inspirations. Finally, if the impression is painful, not only considerable changes of volume, but powerful respiratory movements and disturbance of the voluntary muscles are produced. Disagreeable stimulation produces at first a spasm of the superficial vessels, relaxation of the deep vessels, and decreased fulness of the heart’s contractions. The first two factors together produce a sudden and strong diminution in the volume of the limbs. The last two factors together produce a diminished height of pulse, and in consequence of the enfeebled cardiac contractions there is a stasis of the venous blood showing itself in the increased volume of the limb. These bodily modifications, of which I have summarised the chief features, are commonly regarded as the effects of pain, and this opinion seems even to be accepted in many works on psychology. The opinion cannot, however, be accepted. Pain considered as a psychic event, an internal fact, a pure state of consciousness, is not a cause but a symptom. The cause is the stimulation (of whatever nature) which, coming from the exterior environment, acts on the external senses, or coming from the interior environment, acts on the organic life. It is shown in two ways: on the one hand in the state of consciousness which we call pain, on the other by the physical phenomena above enumerated. The consciousness expresses in one way what the organism expresses in another way. This is not a mere opinion, for experiment shows that circulatory, respiratory, and motor modifications are produced when consciousness is probably defective. Mantegazza has shown that if an intact animal is subjected to pricks, cuts, and burns, cardiac troubles follow; but that the same phenomena are produced after the removal of the encephalon. François-Franck, investigating the effects of painful stimulation on the heart, found that the anæsthesia of chloroform suppresses troubles of the heart, while, on the contrary, removal of the cerebral hemispheres fails to abolish them. Formerly, Longet and Vulpian maintained that in animals reduced to the medulla and lower parts of the cerebro-spinal axis the cries and movements that occur when they are pinched are purely reflex; this interpretation has been contested by Brown-Séquard. In human anencephalic (or headless) monsters, cries, movements of suction and the like have been