The effective dose in these experiments showed considerable variation.
One dog (No. 38) died after a dose of 0.12 gram caffein per kilo, while
some subjects survived doses of 0.2 and 0.23 gram per kilo. In the 12
experiments given in Table 12, page 62, it will be noticed that from
0.12 to 0.152 gram per kilo proved fatal to three dogs, while three
others survived the same amounts in proportion to the body weight. The
results were the same with larger doses. It may be observed in this
connection that in the case of the five dogs in which vomiting was
noticed some time during the 24 hours following the administration
of caffein, four survived, No. 38 being the exception. The greater
toxicity of caffein in this case is in all probability due to some
morbid process, the presence of which was indicated by the high
temperature of this subject.
That vomiting may avert a fatal issue after larger doses of caffein
is made further probable by experiment on dog No. 48, for which, in
the absence of vomiting, a dose of 0.2 gram of caffein per kilo proved
fatal. On this supposition the discrepancy in the results obtained in
this series may be readily explained. The smallest doses which proved
fatal in these experiments were 0.145 and 0.152 gram per kilo. No. 38,
which died from a dose of 0.12 gram per kilo, may be considered as an
exception, as this subject was not normal. Experiments with caffein on
dogs were made at various other times in this laboratory but failed to
show that smaller doses of caffein, even when vomiting did not occur
after its administration, were fatal, although toxic effects were
observed. The conclusion is therefore justified that the minimum fatal
dose of caffein for the normal dog is about 0.15 gram per kilo when
given by mouth.