278   Life and Letters of Francis Galton

uniformity in successive experiments when the pupils are fresh; irregularity and prevalent delay when they are tired. I wish that teachers would often try this simple, amusing, and attractive experiment, and when they have assured themselves that their class enters into its performance with interest and curiosity, they might begin to make careful records at different periods of the day and see whether it admits of being used as a test of incipient fatigue. I should be exceedingly glad to receive accounts of their experiences. Deception must of

course be guarded against.". (p. 160.)

I have not so far come across any data in the Galtoniana, which suggest that any experiences were communicated to Galton.

From the teachers' replies Galton in the memoir draws two conclusions

The first suggests the reason why mental fatigue leaves effects so much more serious than bodily fatigue. When a man is fatigued in body he has many of the same symptoms as arise in mental fatigue, but

"as soon as the bodily exertion has closed for the day, the man lies down and his muscles have rest; but when the mentally fatigued man lies down, his enemy continues to harass him during his weary hours of sleeplessness. He cannot quiet his thoughts and he wastes himself in a futile way." (p. 166.)

I am not clear that this diagnosis is of universal truth, especially in the case of men not habitually used to excessive work. Over physical exertiona fifty-mile walk, or a very strenuous bicycle ride, or a whole day of heavy gardening work-may be followed by muscular fidgets, by unrestrainable fits of shivering, and by actual mental excitement which renders sleep or muscle rest impossible, and the effects may be felt for days afterwards. It says much for Galton's constitution that no experience of this kind seems to have suggested to him that for some individuals bodily and mental fatigue run much the same course'.

The second conclusion that Galton reaches is that breakdowns usually occur among those who work by themselves, and not among pupils whose teachers keep a reasonable oversight. Too zealous pupils are rare. The chief danger occurs when

`°young persons are qualifying themselves for the profession of a teacher, and have also to support themselves and perhaps to endure domestic trials at the same time. Dull persons protect their own health of brain by refusing to overwork. It is among those who are zealous

and eager, who have high aims and ideas, who know themselves to be mentally gifted, and are too generous to think much of their own_ health, that the most frequent victims of overwork are chiefly found." (p. 166.)

There is much in this paper on Mental Fatigue which is of high suggestiveness, and. it should certainly be read by any one planning a more elaborate statistical inquiry into a subject still far from completely explored. The recent discovery and discussion of shell-shock show how large a section of a modern population-and not the least intelligent and zealousbears the terrible load of inherited neuroses. One of the points not touched on in Galton's questionnaire is the family history of those who have suffered serious prostration from mental overwork. We should not be surprised to find a link between this category and that of the shell-shocked. In the

1 It would be of much interest to inquire into the extent to which nervous breakdowns can be directly traced to over strenuous physical exertion.