d by Wedemeyer[310], who found that in the regular administration
of it in the course of four to five weeks there is a measurable
weakening of its action on psychic processes.

Rivers[311], who seems to have been the first to appreciate fully the
genuine and practical importance of thoroughly controlling the
psychological factors that are likely to play a role in such
experiments, concludes that "caffein increases the capacity for both
muscular and mental work, this stimulating action persisting for a
considerable time after the substance has been taken without there being
any evidence, with moderate doses, of reaction leading to diminished
capacity for work, the substance thus really diminishing and not merely
obscuring the effects of fatigue."

EFFECT OF CAFFEIN ON MENTAL AND MOTOR PROCESSES

Schematic Summary of All Results

St.=Stimulation. 0=No effect. Ret.=Retardation.

PRIMARY EFFECT
Small Doses
| Medium Doses
| | Large Doses
| | | Secondary Reaction
| | | | Action Time Hrs.
| | | | | Duration
| | | | | in Hrs.
Process Tests | | | | | |
Motor speed 1. Tapping St. St. St. None .75-1.5 2-4
Coordination 2. Three-hole St. 0 Ret. None 1-1.5 3-4
3. Typewriting
(a) Speed St. 0 Ret. None Results show
(b) Errors Fewer for all None only in total
doses days' work
Association 4. Color-naming St. St. St. None 2-2.5 3-4
5. Opposites St. St. St. None 2.5-3 Next
day
6. Calculation St. St. St. None 2.5 Next
day
Choice 7. Discrimination
reaction time Ret. 0 St. None 2-4 Next
day
8. Cancellation Ret. ? St. None 3-5 No