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and one to which science has not yet furnished a satisfactory solution. The question of adequate treatment for these cases must obviously await that solution. At present it seems possible to accomplish something both by physiological and psychological methods of treatment, but until the various causal factors and their mode of action have been determined it is impossible to say which of these methods will ultimately prove to be the most effective. The great need here is for investigation and research. The problem must be attacked from every side, by the physiologist, the chemist, the anatomist and the psychologist, in the sure hope that their united labour will finally elucidate these causal factors, and indicate the ways in which they may be eradicated.
But there is one group in which it is becoming more and more certain that "mental" factors constitute the most important link in the chain of causation, and that is the group which we have called "nervous disorders." We have, indeed, reached the paradoxical conclusion that, while in many "mental" disorders mental factors play only a minor part amongst the causes which have produced them, in "nervous" disorders these mental factors are of fundamental significance. In this latter group the chain of causation will appear as in the diagram below:
The conviction that in the so-called nervous dis-
