"Pavlov’s findings were confirmed in the most distressing manner, and on a very large scale, during the two World Wars. As the result of a single catastrophic experience, or of a succession of terrors less appalling but frequently repeated, soldiers develop a number of disabling psycho-physical symptoms. Temporary unconsciousness, extreme agitation, lethargy, functional blindness or paralysis, completely unrealistic responses to the challenge of events, strange reversals of life-long patterns of behaviour—all the symptoms, which Pavlov observed in his dogs, re-appeared among the victims of what in the First World War was called ‘shell shock’, in the Second, ‘battle fatigue’. Every man, like every dog, has his own individual limit of endurance. Most men reach their limit after about thirty days of more or less continuous stress under the conditions of modern combat. The more than averagely susceptible succumb in only fifteen days. The more than averagely tough can resist for forty-five or even fifty days. Strong or weak, in the long run all of them break down. All, that is to say, of those who are initially sane. For, ironically enough, the only people who can hold up indefinitely under the stress of modern war are psychotics. Individual insanity is immune to the consequences of collective insanity."