_Guinea pig 67. Gray and yellow male. Weight, 330 grams. Diet,
oats._
October 5: 11.25 a. m., 4 cc of 2 per cent caffein injected into
peritoneal cavity (240 mg per kilo); 11.30 a. m., tetanus--survived,
convulsions off and on. Death at 2.55 p. m. _Autopsy_: Severe
gastroenteritis; kidney petechiated; congestion of lungs and liver.
_Guinea pig 63. Gray and white male. Weight, 340 grams. Diet, oats._
October 5: 11.20 a. m., 4 cc of 2 per cent caffein (235 mg per kilo)
injected into peritoneal cavity.
October 14: Alive and in good condition.
_Guinea pig 64. Brown and black female. Weight, 305 grams._
October 5: 11.35 a. m., 3.8 cc 2 per cent solution caffein (250 mg per
kilo) injected into peritoneal cavity; 11.40 a. m., tetanus--survived,
convulsions off and on, died at 4.15 p. m. _Autopsy_: Findings exactly
the same as in No. 67.
Examination of the results of the experiments by intraperitoneal
injections showed that 0.2 gram caffein per kilo was toxic in
two guinea pigs (Nos. 59 and 58). Severe symptoms were observed
within 15 minutes in No. 56 and within one hour in No. 55 after the
administration of approximately the same dose of caffein. One of
these died within three and one-half hours; the other, No. 56, made
a good recovery from the acute effects. This amount of caffein may
be regarded, therefore, as the minimum toxic dose for the guinea pig
when injected into the peritoneal cavity. This is corroborated by
the experiments of series B in which smaller doses failed to show
any muscular, nervous, or respiratory symptoms, nor were there any
after effects noticed, as all of them survived and were kept under
observation for some time. The guinea pigs of series A, however, seem
to contradict these results. It will be remarked that appreciably
smaller doses induced symptoms in all of them, and one case terminated
fatally. The seasonal variation, as already pointed out, is in all
probability likewise responsible for the difference in the resistance
between the guinea pigs of series A and B. Tests were made also to
determine the minimum fatal dose. For this purpose the experiments of
series D were performed. The resistance of No. 63 in this series is
quite striking. We are unable to explain such a discrepancy in the
results obtained under practically uniform conditions. The minimum
fatal dose of caffein, when injected into the peritoneal cavity, is
therefore about 240 to 250 milligrams per kilo. These amounts, it will
be observed, were rapidly fatal, in striking contrast to the results
obtained when such doses were injected subcutaneously. This is probably
due to a better absorption from the peritoneal cavity than from the
subcutaneous tissues.