In the two experiments of this series the rate of injection as a
possible factor influencing the toxicity of caffein was tested. A 2
per cent caffein solution was injected at the rate of 1 cc in two and
one-half to three minutes.
_Rabbit 572. Gray male. Weight, 1,770 grams. Diet, oats._
February 8: Injection began at 3 p. m., discontinued at 3.37 p. m., and
resumed at 3.38 p. m.; rabbit was restless; injection finished at 3.52
p. m. Total quantity received, 17.4 cc 2 per cent caffein intravenously
in 52 minutes; struggled intermittently during the injection; anterior
legs paralyzed.
February 9: Found dead.
_Rabbit 573. Gray male. Weight, 1,810 grams. Diet, oats._
February 8: Started to inject at 1.35 and discontinued at 2.27 p. m.;
received 18 cc 2 per cent caffein intravenously in 52 minutes; reflexes
markedly increased soon after; 2.45, passed bloody urine; 4.30 p. m.
reflexes increased; no other symptoms.
February 9: 9 a. m., found dead.
It will be observed that some retardation of the onset of symptoms
was caused by slower injection, but the final result was the same as
when the injections were made more rapidly. It is quite probable,
therefore, that a much slower rate of injection may lessen considerably
the toxicity of caffein.
From the results of the experiments by intravenous injection summarized
in the table, it appears that the minimum toxic dose for rabbits of a
2 per cent caffein solution, injected at the rate of 1 cc per minute,
is about 50 mg per kilo. Twice the dose induces severe symptoms and may
be fatal; 160 mg per kilo are surely fatal. If the rate of injection
is diminished, the toxicity of caffein is lessened, but this effect
is not marked unless the injections are very slow. Dilution of the
caffein solution suppresses to some extent the nervous symptoms, but
the toxicity, on the contrary, seems to be increased.