Page:Popular Science Monthly Volume 6.djvu/581

Rh This change depends upon physical conditions, and a more pronounced physical state not only involves the emotional centres, but implicates the intellectual processes. Thus, a slight amount of bile in the blood, or an excess of renal products, may depress a man with hopeless despair or drive him into paroxysms of violent passion. The delirium of fever is a familiar instance of the influence exercised by passing bodily conditions upon the brain and its product—thought.

When the nutrition of the brain is good, we experience an agreeable sense of well-being, which shows itself distinctly in after-dinner geniality. When the nutrition is imperfect, or the arterial blood is of abnormal composition, the consequences are a mixture of irritability and bad temper, blended with depression. We are all familiar with the crossness of the hungry man; when fasting, crossness is interchangeable with hunger—is often its substitute, and forms a contrast with the amiability of repletion. Especially is this irritability seen in those whose digestive powers are weak. A similar irritability is the ordinary mental attitude of convalescence from acute disease, and either precedes or runs into and coexists with the keen appetite usually found at that time. They are linked together by something more positive than coincidence.

The dependence of modifications of the functional activity cf the cerebral cells upon other corporeal conditions than changes in the blood is now well recognized. There are communicating fibres by which the brain receives impressions of varying character from different organs. An impression coming in from some far-away point stimulates or inhibits the action of the cerebral cells. So strong may be the impression that actual insanity may result, as in the case, related by Schroeder van der Kolk, of a lady who became insane whenever her womb became displaced, and sane again as soon as it was returned to its place.

The effect of several morbid states is to stimulate the brain into greater activity. A non-medical but most acute observer and able writer says: