These experiments were carried out on two varieties of rabbits, the
white and the gray. The diet consisted chiefly of oats, but in a few
cases carrots formed the exclusive diet. Food and water were given ad
libitum. A 2 per cent solution of caffein was administered through a
stomach tube. Since the resistance to most drugs is commonly supposed
to be greater when given by mouth than when administered by any
other path, doses of 175 to 200 mg per kilo were fed in a series of
preliminary experiments, all of which were performed on gray rabbits
weighing from 865 to 1,135 grams, and which were fed carrots for
several days previous to the experiment. Three of the rabbits survived,
two without showing any symptoms; in the other case paralysis of the
posterior extremities was observed five hours after he received caffein
and he was found dead the next morning. Unfortunately no autopsy was
performed. The low resistance to caffein of this animal was probably
due to some abnormal condition which developed about the time of the
experiment, since this rabbit received 325 mg of caffein per kilo
two weeks previously and increased reflexes only were observed as a
result of this treatment. Hence 200 mg of caffein per kilo can not
be considered the toxic dose when fed by mouth. In the following
experiments larger doses were therefore given.