As already pointed out in the experiments on acute toxicity of caffein,
young growing dogs are probably more resistant to caffein than adults.
That this may also hold true in chronic caffein intoxication seemed
indicated by the following experiments.
_Dog 33. Black female puppy. Weight, 4 kilos. Had been continuously
on a meat diet._
December 22: 2.30 p. m., received 0.69 gram of caffein (0.172 gram per
kilo); 3.15 p. m., no symptoms except that feces were fetid.
December 23: 11.30 a. m., received 0.79 gram of caffein (0.197 gram per
kilo); 1.30 p. m., no symptoms.
December 24: 11 a. m., received 0.87 gram of caffein (0.2009 gram per
kilo); 4 p. m., no symptoms.
It will be observed that the only effect produced in dog 33 by feeding
caffein was increased intestinal putrefaction, although 2.37 grams
of caffein were given in three days. Additional data on the effects
of the age of animals on the resistance to caffein seemed desirable.
The following experiments were therefore carried out. Six puppies of
the same litter were weaned when 7 to 8 weeks old and put on a milk
diet. Three of them received this diet throughout the experimental
period. Meat was substituted in the other three a few days before the
administration of caffein was begun, and was continued until the end of
the experiment. Caffein was given by mouth; the initial dose, which was
administered for several days and then gradually increased, being 160
to 200 mg for each dog, except one, which received only 100 mg per kilo
for several days and then an increased amount.
An intermission of a few days (during which no caffein was given) was
allowed. This was done on account of some studies carried on at the
same time on the effect of caffein on certain constituents of the urine.