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by the explosion of a tear-shell, and is then due to the irritative action of certain gases liberated by the bursting of the shell. It may also be produced by the loss of a loved relative, and is then due to the presence in the mind of certain ideas, and the emotions associated with those ideas. In the first case we should say that the cause of the weeping was physical, in the second that it was mental. Or again, irritability may result from noxious substances in the blood arising as a result of dyspepsia, or it may be due to the patient being absorbed in anxious consideration as to which of two conflicting lines of conduct he should adopt. In the first case the irritability is of physical, in the second of mental origin.
As a result of this brief historical investigation we find, therefore, that there are two conceptions of the origin of mental and nervous disorders which at present hold the field, the "physiological" and the "psychological" According to the first, the phenomena are to be interpreted as the effect of a chain of physical or physiological causes, diseases of the brain and other organs, or the presence in the body of poisonous substances. According to the second, they are to be interpreted as the effect of a chain of mental causes, worries, anxieties, emotions and so forth. Hence the question arises: Which of these conceptions is to be accepted in the light of modern knowledge? Are we to embrace the doctrine that mental and nervous disorders result from such causes as brain diseases and poisons in the blood, or the rival doctrine that they are due to such things as
