The object of these experiments was to determine the resistance to
caffein in various species of animals and by various methods of
administration. Caffein was therefore given by mouth and injected
subcutaneously into the peritoneal cavity, into the muscles, and
intravenously. As far as could be judged by appearance, healthy
animals were selected for the subjects of the experiments, but as it
is impossible to diagnose with any degree of accuracy the condition of
the animal while it is alive, post mortem examinations were resorted
to in many cases in which the issue of the experiment was fatal. Since
the age of the animal may modify toxicity full grown, as well as young,
animals were employed for these experiments; diet, race, and season
also play an important part in determining the toxicity of a drug and
these factors were also taken into account in the present investigation.