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as in a short time there will be very little diphtheria, and less 
consumption, for the Medical Officer to talk of by day and dream 
by night, I would suggest that his attention be directed to the 
cause and, when possible, to the prevention of strain and fatigue. 
A certain amount of strain will always be inevitable both in youth 
and manhood, but all unnecessary fatigue, or what I would 
venture to call unproductive strain, should be prevented. 
Street noises, especially night noises, are one fertile source of 
unproductive strain. ‘Think of the loss of nerve energy that may 
be caused by a dozen or more thoughtless youths shouting to each 
other at 4.30 on a Sunday morning. Probably by that noise in 
the early morning several people would be roused, and would 
lose an hour or more of sleep, and so energy would be dissipated 
with no work produced. That is only oe illustration of 
unnecessary, unproductive loss of energy ; it would not be difficult 
to point out others. 
Brain.—Roughly, the brain is one-fortieth of the body 
weight ; but mass for mass it has by far the largest blood supply 
in the body. Besides several small arteries, it has four very large 
vessels: two Zz¢ Carotids and two Vertebrals. Its blood supply 
therefore is as great as that of the two legs and thighs. This will 
give you some clue as to the amount of work Nature expects of 
this organ, and her provision against fatigue. 
As I shall find it impossible to touch but a few points in this 
branch of my subject, I have classified the causes of mental 
fatigue, and, of course, the same classification will apply to 
physical fatigue. 
It may be caused by :-— 
(1) An adnormal amount of work, in otherwise normal 
conditions. 
(2) A normal amount of work but carried out in 
abnormai conditions. 
(2) Worst of all, an adnormal amount of work in 
abnormal conditions. 
Of course the xorma/ or abnormal amount of work are purely 
relative terms. What would be an easy task for one man or child 
would be hard work to another. 
The abnormal state or environment may be caused by 
certain well known physical states of health, or want of health, 
that are inimical to mental work, viz., by errors of diet, either in 
kind or in quantity ; by too little, or too much exercise ; by states 
of temperature, or ventilation. These are quite obvious causes 
of a vicious environment, and would occur to the minds of all. 
But that the keen edge of one’s intellect can be blunted by the 
condition of the nose and throat is not quite so obvious, but it is 
just as true. This abnormal condition applies more to children 
than to adults, but may be found also in the latter. It has been 
rs 
