A 0.5 per cent caffein solution was used in these experiments in order
to test the effect of concentration on its toxicity; the rate of
injection was 1 cc per minute.
_Rabbit 569. Gray male. Weight, 1,475 grams. Diet, oats._
February 6: 11.50 a. m. to 12.01 p. m., injected 10 cc 0.5 per cent
caffein; 12.03 to 12.12 p. m., injected 10 cc of 0.5 per cent caffein;
12.13 to 12.26 p. m., injected 10 cc of 0.5 per cent caffein, total
amount injected, 30 cc; 12.20, passed 35 cc of urine; 12.30, increased
reflexes, but no convulsions; 4 p. m., reflexes increased.
February 11: Alive, condition good.
_Rabbit 574. Gray female. Weight, 1,555 grams. Diet, oats._
February 8: 10.25 to 10.33 a. m., injected 4 cc of 0.5 per cent caffein
in salt solution, injection discontinued for five minutes; 10.38 to
11.10, injected 30 cc, total amount of caffein solution received, 34
cc; 11.55 a. m., very sensitive; reflexes markedly increased.
February 9: Alive, condition good.
_Rabbit 571. Gray female. Weight, 1,530 grams. Diet, oats._
February 7: Injection 3.18 to 3.50 p. m., received 30 cc in 32 minutes,
not hypersensitive; 3.55, restlessness and weakness of extremities;
4.10 p. m., control of anterior extremities impaired, distinctly
paretic but tried to walk about, died the same afternoon.
_Rabbit 568. Gray male. Weight, 1,605 grams. Diet, oats._
February 7: Injection 10.53 to 11.01 a. m., injected 10 cc 0.5 per cent
caffein; 11.03, injection resumed after two minutes interval; 11.14,
received 10 cc 0.5 per cent caffein intravenously in 11 minutes; 11.16,
injection resumed; 11.35, received 12 cc 0.5 per cent caffein, total
amount of caffein solution received, 32 cc; 12.30 p. m., urinated 14
cc of bloody urine; 12.55 p. m., convulsions and death a few minutes
later. Autopsy showed congestion of viscera, but no other lesions.
_Rabbit 570. Gray female. Weight, 1,225 grams. Diet, oats._
February 7: 2.06 to 2.35 p. m., injected 24.5 cc 0.5 per cent caffein,
reflexes increased but no convulsions, paresis especially marked in
the anterior extremities; 3 p. m., passed urine which was normal in
appearance, reflexes not increased but rabbit was weak.
February 9: Found dead. _Autopsy_: Liver, spleen, and kidneys
congested; large intestines hemorrhagic; omentum congested and showed
the presence of small caseous nodules; liver showed adhesion to
diaphragm; viscera presented the appearance of intraabdominal infection.
Of the five rabbits of this series three died as a result of the
administration of caffein. The other two which survived showed mild
symptoms only, such as increased reflexes, but no evidence of severe
poisoning such as was observed after the injection of the same doses of
caffein in series A when a 2 per cent solution of caffein was injected.
Convulsions were noticed in one case only (No. 568); paresis in two
cases (Nos. 570 and 571). The nervous symptoms even in this group,
therefore, were much milder than in series A. The percentage of death,
however, was greater than in series A, in which the concentration of
caffein was four times as great. It is quite probable that the strain
on the heart due to the sudden increase in volume of the blood and
its dilution might be an important factor in increasing the toxicity
of caffein. It is conceivable that doses just sufficiently large to
depress the normal heart may cause paralysis of an already overstrained
organ.