e effects of coffee drinking have been attributed to
this alkaloid, a brief presentment of the pharmacology of caffein will
be given as an exposition of the many statements made regarding it.
According to the _British Pharmaceutical Codex_[257]:

Caffein exerts three important actions: (1) on the central nervous
system: (2) on muscles, including cardiac: and (3) on the kidney.
The action on the central nervous system is mainly on that part of
the brain connected with psychical functions. It produces a
condition of wakefulness and increased mental activity. The
interpretation of sensory impressions is more perfect and correct,
and thought becomes clearer and quicker. With larger doses of
caffein the action extends from the psychical areas to the motor
area and to the cord, and the patient becomes at first restless and
noisy, and later may show convulsive movements.

Caffein facilitates the performance of all forms of physical work,
and actually increases the total work which can be obtained from
muscle. On the normal man, however, it is impossible to say how
much of the action on the muscle is central and how much
peripheral, but, as fatigue shows itself first by an action on the
center, it is probable that the action of caffein in diminishing
fatigue is mainly central. Caffein accelerates the pulse and
slightly raises blood pressure. It has no action in any way
resembling digitalis; by increasing the irritability of the cardiac
muscle, its prolonged use rather tends to fatigue than to rest the
heart.

Caffein and its allies form a very important group of diuretics.
The urine is generally of a lower specific gravity than normal,
since it contains a lesser proportion of salt and urea; but the
total excretion of solids, both as regards urea, uric acid, and
salts, is increased. Caffein, by exciting the medulla, produces an
initial vaso-constriction of the kidneys, which tends at first to
retard the flow of urine. So in recent years, other drugs have been
introduced, allies of caffein, which act like it on the kidneys,
but are without the stimulant action on the brain. Theobromine is
such a drug.

Another authority states that[258]:

One of the most constant symptoms produced in man by over-doses of
caffein is excessive diuresis, and experiments made upon th