ity
or change of activity, or nearly complete inactivity as in
sleep, are not only desirable but necessary, if efficiency is to be
maintained. The demand for rest is an imperative physiological
demand. The amount of recuperation demanded by
the organism varies in different individuals, but that there are
certain limits of human productivity has been made increasingly
clear by a careful study of the effects of fatigue upon
output in industrial occupations. Repeatedly, the shortening
of working hours, especially when they have previously numbered
more than eight, has been found to be correlated with
an increase in efficiency. Likewise, the provision of rest
periods as in telephone-operating and the needle trades, has in
nearly every case increased the amount and quality of the
work performed. The human machine in order to be most
effective cannot be pressed too hard. A striking illustration
was offered in England at the beginning of the war. Under
pressure of war necessity, the munition factories relaxed all
restrictions on working hours and operated on a seven-day
week. The folly of this procedure was tersely summarized by
the British Commission investigating industrial fatigue,
which reported: "It is almost a commonplace that seven days'
labor produces six days' output."

In the study of industrial conditions, the effects of prolonged
and repeated fatigue upon output have not been the
only features taken into consideration. Not only are there
immediately observable effects in the decreased output of the
worker, but fatigue means, among other things, general loss
of control. This has the effect of producing on the part of
overworked factory hands dissipation and overstimulation in
free time, with a consequent permanent impairment of efficiency.[1]
Both for the laborer himself and for the efficiency
of the industrial system, it has been increasingly recognized
that limitation of working hours is imperatively demanded.
Rest is as fundamental a need as food, and its deprivation
almost as serious in its effects.

[Footnote 1:
For a striking array of testimony on this point see Goldmark: _loc. cit._,
pp. 220-35.]

NERVOUS AND MENTAL FATIGUE. The conditions of nervous
and mental fatigue have been less adequately studied than
the types of purely physiological fatigue just discussed. It is
difficult in experiments to discount the effects of muscular
fatigue, and to discover how far there is really impairment of
nervous