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to come on, if the morning paper started at nine, and ended at 
twelve, and then an interval allowed of two or three hours before 
starting another three hours work ; or, if that change could not be 
made, why not substitute another subject for the afternoon, and 
save the subject of geometry for the next morning, when the brain 
would be fresher to deal with it. A change of work is sometimes 
as good as a rest. 
Physiologists can’t say with certainty how much fatigue the 
brain can bear without damage, nor at what age it can endure 
fatigue without danger. 
It must be.remembered that fatigue, either muscular or 
mental, probably bears the same relationship to acute diseases as 
chill does. It is relatively much more dangerous to come into 
contact with infectious diseases in the evening, when the vital 
forces are fatigued, than in the morning, when the same forces are 
fresh, and have greater resisting power. And as regards the more 
chronic illnesses, especially of nerve type, there is no more potent 
factor than fatigue. It is well known that a long spell of sick 
nursing, continued with loss of rest, in one unaccustomed to that 
work, will produce such a state of exhaustion of the nervous 
system as to permanently damage the general health. It is 
equally well known that that part of the body which is most 
fatigued is most prone to disease. I have always looked upon 
boils and carbuncles as evidence of fatigue, and have been able to 
collect some remarkable cases in support of that opinion. 
There is a concurrence of opinion that before the sixth year 
it is not well for children to work in school. On the other hand 
moderate mental exercise conduces to the development of the 
brain. It has been shown that school is one of the most effective 
means of ameliorating the condition of cretins in places where 
cretinism exists endemically. A brain must be made to work, 
just as a field must be cultivated, in order to prevent it from 
running wild, but the moment study becomes exhausting it ceases 
to be useful. One ought to exercise the brain constantly, but 
never to exhaust it. When one looks into it, the function of 
fatigue of the brain is an immense subject, and one which it is 
impossible to touch but the fringe of it in an hour’s paper. There 
are certain well defined laws which should govern all head workers 
and are applicable to all of us; but outside these every man must 
be a law unto himself. 
(x). Hard mental work should not be attempted after a full 
meal; nor when hungry; nor when very cold; nor when very 
tired ; nor in the convalescent stage of an illness, especially if 
that illness has been influenza. I have known cases of most 
severe headache coming on and lasting for months from this 
cause, and one has only to study the daily papers to know how 
frequently a mental collapse is attributable to this illness. 
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