since in the adult the learning and re-learning aspects are not of
importance unless we wish to get some index of an individual's
plasticity. This distinction between the genetic or acquisition
phase of any activity and its later exercise has led to some con-
fusion in psychology.

The efficiency of these organized functional systems never
changes very much in the adult. They are not practiced suffi-
ciently at any one time or under the right conditions for any
great improvement to occur. On the other hand, they are used
so frequently that the memory loss is insignificant after a period
of no practice. As adults we are on a permanent plateau with
respect to the efficiency of most customary acts: that drugs, lack
of oxygen, emotional disturbances and environmental changes in
general can produce greater or less fluctuations in efficiency,
temporary in character, will now appear.

"Fatigue" Not a Serviceable Conception in Psychology.--
Probably the most essential thing for the beginning student to
do or for any scientific man planning to do research in the field
of human work is to neglect most of the general discussions which
have gathered around the subject of fatigue. James somewhere
says about emotion: "But as far as 'scientific psychology' of the
emotions goes I may have been surfeited by too much reading of
classical work on the subject, but I should as lief read verbal
descriptions of the shapes of the rocks on a New Hampshire farm
as toil through them again." Much the same could be said
about fatigue. The literature from the standpoint of discussion
is complex and confusing and worthless both because it is not
constructive and because it deters men from engaging in the study
of the factors influencing the curve of work. Three reasons
can be advanced for this condition: (1) and most important,
confusion starts the moment the human animal is dissected into
a so-called "mental" worker and "physical" worker. This is a
most pernicious way of splitting up human activity. No matter
what the human animal is doing he works as a whole. What
measure of truth is to be found in this division can be better
formulated by saying that certain activities, like splitting wood
or dragging a cannon over muddy ground, demand the func-

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