The fundamental causes acting on Prisoners of War are loss of liberty, the herding together of large numbers, the unknown duration of captivity. They suffer from want of space, the impossibility of isolating themselves from their fellows, the constant expectation in which they live whilst awaiting letters or parcels, and the ever recurrent disappointments connected therewith; and all these sufferings are accentuated by that important factor, ignorance of the duration of captivity. At the outset the prisoners seek in febrile activity a release from all these sufferings, which are aggravated by the memories of horrors lived through, apprehensions regarding the future, and nostalgia for country and relatives. Schools, theatrical performances, and concerts are organized; but gradually the exterior world effaces itself and disappears, and the prisoners live in a shadow land, without colour or life. Sensations are blunted, and give place to apathy, and the events of the war are followed with a mediocre interest. Such is the _milieu_ in which neurasthenia develops, well marked in some, less so in others, but common to all those who have passed six months in captivity behind wire barriers, and reaching a special intensity amongst, roughly speaking, 10 per cent. of the captives. First of all, an exaggerated irritability manifests itself, and the least opposition becomes insupportable. Quarrels are frequent. Then intellectual concentration becomes difficult, and such as renders close attention to a few pages of a book impossible. In such cases the prisoner often deliberately gives up his promenades, and prefers to remain quiescent. A phenomenon of constant occurrence is the loss of memory, and inability to recall names of persons or of localities, specially those connected with memories anterior to the war. A Sergt.-Major, for instance, forgot the name of the Colonel who commanded his regiment since 1913, and has been unable to recall it up to the present. Several Interned cannot remember the Christian names of their fathers, mothers, and other near relatives. Another cannot recall the name of his village. Such cases are numerous even amongst those who have been in Switzerland for eighteen months. As a symptom of a secondary nature, insomnia may be mentioned, though this varies. It may play a rôle in one camp, and not in another. Some prisoners complain of a loss of sight, and many become extremely suspicious and defiant. All have a marked tendency to regard the ordinary events of their daily life from a distorted point of view. The chief sufferers become silent for three or four days at a time, and are plunged in a sort of torpor. Once this state is established, it becomes in general stationary, and does not diminish as long as the captivity lasts.