data
9. S-W illusion 0 0 0
General 10. Steadiness ? Unsteadiness None 1-3 3-4
11. Sleep quality Individual differences
12. Sleep quantity depending on body weight 2 ?
13. General health and conditions of
administration

Subsequent to these investigations was that of Hollingworth[312] which
is at once the most comprehensive, carefully conducted, and
scientifically accurate one yet performed. He employed an ample number
of subjects in his experimentation; and both his subjects, and the
assistants who recorded the observations, were in no wise cognizant of
the character or quantity of the dose of caffein administered, the other
experimental conditions being similarly rigorous and extensive.

The purpose of his study was to determine both qualitatively and
quantitatively the effect of caffein on a wide range of mental and motor
processes, by studying the performance of a considerable number of
individuals for a long period of time, under controlled conditions; to
study the way in which this influence is modified by such factors as the
age, sex, weight, idiosyncrasy, and previous caffein habits of the
subjects, and the degree to which it depends on the amount of the dose
and the time and conditions of its administration; and to investigate
the influence of caffein on the general health, quality and amount of
sleep, and food habits of the individual tested.

To obtain this information the chief tests employed were the steadiness,
tapping, coordination, typewriting, color-naming, calculations,
opposites, cancellation, and discrimination tests, the familiar
size-weight illusion, quality and amount of sleep, and general health
and feeling of well-being. A brief review of the results of these tests
is given in the tabular summary.

From these Hollingworth concluded that caffein influenced all the tests
in a given group in much the same way. The effect on motor processes
comes quickly and is transient, while the effect on higher mental
processes comes more slowly and is more persistent. Whether this result
is due to quicker reaction on the part of motor-nerve centers, or
whether it is due to a direct peripheral effect on the muscle tissue is
uncertain, but the indications are that caffein has a direct action on
the muscle tissue, and that this effect is fairly rapid in appearance.
The two pr