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called "functional" as opposed to "organic"— that is to say, those not due to any demonstrable disease or injury of the nervous system. These conditions are covered by a multitude of popular names: "neurasthenia," "hysteria," "nervous breakdown" and just "nerves." The war has added yet another to this list, for the now familiar "shell shock" is merely a general term under which are grouped a large number of the cases of nervous disorder due to the stress of active service.
Defined in this way, "mental and nervous disorder" constitutes a heterogeneous group of affections, many of which are very different one from another, but we are justified in considering them together, because in every case mental phenomena play a part either in the symptoms or in the causation. So far as the mental group is concerned this fact is obvious, and we shall see that we now have reason to believe that the statement is equally true in the case of the so-called nervous group.
The treatment of these disorders forms a fascinating chapter in the history of medicine, and it will be worth while to spend a few moments in perusing that chapter, because our understanding of the present will be materially helped by some knowledge of the views and practices of the past. Treatment has naturally depended always on the current opinion with regard to causation, and the extraordinary diversity of practice throughout history in dealing with these cases has been the logical result of the constant change of view as to the causes responsible for them.
In the Middle Ages the phenomena which we now
