2. The influence on respiration is more irregular and more unstable; the rhythm becomes abnormal, sometimes rapid, sometimes slow; the inspirations are successively short and deep. But the final result is a notable diminution in the carbonic acid exhaled—that is to say a real slackening of combustion. The temperature is lowered. “I had imagined,” says Mantegazza, “that pain would be accompanied by an increase of heat, muscular action being very intense under the influence of great suffering. Experiment on animals and on myself proved the contrary.”[17] Heidenhain and Mantegazza have in fact noted an average diminution of two degrees centigrade, which, according to the latter, may last an hour and a half or more; it would be due to the contraction of the peripheral blood-vessels. ----- Footnote 17: Mantegazza, _Fisiologia del Dolore_, chap. iii. ----- 3. The action of pain on digestion is well known, and shows itself by retardation or disturbance: loss of appetite, arrest of secretions, indigestion, vomiting, diarrhœa, etc. If permanent it acts on the general nutrition, and shows itself in modifications of the urinary secretion, and lasting discoloration of the skin or hair. It is not infrequent to find blanching of the hair, the beard or eyebrows in a few days under the influence of great pain.[18] ----- Footnote 18: For historical and other cases, see Hack Tuke, _Influence of the Mind upon the Body_, chap. iii. ----- 4. The motor functions translate pain in two opposite ways: the passive form of depression, arrest, or total suppression of movements, in which the patient seems overcome; the active form, marked by agitation, contortions, convulsions, and cries. The latter case seems to contradict the general formula connecting pain with diminished activity, and seems to me to have been misinterpreted by some authors. This violent excitement, indeed, is an expenditure which quickly makes itself felt and soon leaves the individual enfeebled. It does not flow, as in joy or play, from a surplus of activity; it is weakening, irregular and spasmodic. It seems to me to originate in the instinctive expression of the emotions. The wounded animal shakes the painful part of his body, his paw or his head, as if trying to expel the suffering. All these disorderly and violent motor reactions are a defence of the organism, a useless and often hurtful defence, but resulting from acts which, formerly or under other circumstances, were adapted to their end. Lehmann experimented on five persons, submitting them in turn to agreeable and disagreeable impressions, in both cases registering the changes in respiration and in the volume of the arm with the help of Mosso’s plethysmograph.[19] His experiments led him to the following conclusions:— ----- Footnote 19: For details of the experiments see _Hauptgesetze_, etc., pp. 77 _et seq._, with the accompanying graphic traces. -----