The physiologist is able to furnish a great variety of illustrations of the effect of Physical Conditions over Mental States. He shows that many cases of mental trouble are due to eye-strain, and other muscular disturbances, and that serious mental complaints sometimes arise by reason of physical lesions. The very terms used to designate certain abnormal mental states show the relation, as for instance, _melancholia_ which is derived from the Greek words meaning "black bile"; and _hysteria_, which is derived from the Greek word meaning "the womb; or uterus." Every one knows the Mental States produced by a sluggish liver, or by dyspepsia, or from constipation. We all know the difference between our mental capacity for thinking when we are tired, as contrasted with that accompanying the refreshed physical condition. No man, whatever his philosophy, can truthfully claim to be able to maintain a placid, even disposition, and a perfectly controlled temper, when he is suffering from a boil on the back of his neck. And, all know that after indulging in the midnight "Welsh rarebit," one is apt to dream of his grandmother's ghost, or see dream elephants with wings. All know the delirium produced by overindulgence in liquor, and the hallucinations that accompany fever. The effect of drugs, tobacco, and alcohol upon the Mental States are well known. "Philip drunk" is a very different mentality from "Philip sober." The Mental States accompanying particular diseases are well known to physicians. One disease predisposes the sufferer to gloominess, while another will induce a state of feverish hilarity. Some leading authorities now hold that many cases of insanity are really due to abnormal conditions of the blood, rather than to any diseased condition of the brain.