The object of the experiments of this series was to study the effect of
age on the resistance to caffein. Half-grown rabbits were, therefore,
used in the following experiments.
_Rabbit 310. Belgian hare, female. Weight, 880 grams. Diet, oats._
March 2: 3.25 p. m., 9 cc 2 per cent caffein (0.2 gram per kilo)
injected into peritoneal cavity.
March 3: 9.30 a. m., no symptoms, rabbit looks normal.
March 4: 11 a. m., posterior extremities abducted, walked when placed
on the floor, made no attempt to change attitude when placed on its
side, remained some time in this position.
March 5: 9 a. m., found dead. _Autopsy_: Liver showed areas of
degeneration; kidneys congestion and petechial hemorrhage on cortex;
small and large intestines, inflammation marked; bladder distended.
_Rabbit 75. Gray and white, female. Weight, 842 grams._
January 25: 3 p. m., 8.5 cc 2 per cent caffein solution (0.2 gram per
kilo) injected into peritoneal cavity; 3.15 p. m., anterior extremities
weak and reflexes increased.
January 27: Rabbit paralyzed but is able to turn over when placed on
back.
_Rabbit 74. Gray and white, female. Weight, 692 grams._
January 25: 3 p. m., 7 cc 2 per cent caffein (0.2 gram per kilo)
solution injected into peritoneal cavity; 3.15 p. m., reflexes
increased and anterior extremities paralyzed.
January 27: Rabbit recovered and is able to walk about in the room.
_Rabbit 312, maltese, female. Weight, 740 grams. Diet, oats._
March 3: 11.47 a. m., urine obtained from bladder, appearance normal,
no albumen, no reduction of Fehling's solution; 11.50 a. m., 7.5 cc 2
per cent caffein (0.2 gram per kilo) injected into peritoneal cavity;
2.30 p. m. anterior extremities paralyzed, posterior extremities rigid
and extended; 5 p. m. (about), rabbit died.
_Rabbit 311. Belgian hare, female. Weight, 650 grams. Diet, oats._
March 3: 11.26 a. m., urine obtained from bladder normal in appearance,
albumen considerable, reduction of Fehling's solution none; 11.27 a. m.,
6 cc 2 per cent caffein solution (0.2 gram per kilo) injected into
peritoneal cavity; 2.30 p. m., rabbit seemed to be normal, no symptoms
had developed; urine collected contained a large amount of sugar,
reduction was very heavy, but no albumen was found.
March 4: 11 a. m., condition good, moves about when put on floor; gait,
normal.
_Rabbit 78. Yellow and white. Weight 659 grams._
January 26: 1.30 p. m., 8.5 cc 2 per cent caffein (250 mg per kilo)
injected into peritoneal cavity, under observation the rest of the
afternoon, no symptoms.
January 27: 4 p. m., no symptoms developed.
_Rabbit 317. Belgian hare, female. Weight 635 grams. Diet oats._
March 15: 10.35 a. m., 8 cc 2 per cent caffein (0.252 gram per kilo)
injected into peritoneal cavity; 12 noon, marked abduction of hind
legs, was unable to walk after a little exertion, rabbit died between
12.30 and 12.50 p. m. _Autopsy_. Right lung hepatized and showed
adhesions to costal and mediastinal pleura; liver studded with nodules
of coccidiosis; spleen congested; stomach filled, mucosa normal;
intestines injected; colon hemorrhagic on serosa in ventral region,
near point of injection; kidneys normal.
_Rabbit 323. White, female. Weight 820 grams. Diet oats._
March 15: 10.45 a. m., 10 cc 2 per cent caffein (250 mg per kilo)
injected into peritoneal cavity; 12 noon, reflexes increased, hind legs
abducted but is able to walk, symptoms are mild; 1.40 p. m., tremors,
weakness, and abduction of head and legs much more marked than at 12
noon.
March 16: Condition good.
March 17: Condition good, recovery apparently complete.
Since the experiments of Series A, which were intended as preliminary
tests, have shown that 0.3 gram of caffein per kilo when introduced
into the peritoneal cavity is rapidly absorbed and is fatal, much
smaller doses were employed in subsequent trials with the drug. This
is shown in series B, which may be divided into two groups. Group I,
consisting of rabbits 69, 70, 92, 93, and 309, which received 0.2
gram of caffein per kilo, and Group II, Nos. 307 and 308, into which
0.15 gram of caffein per kilo was injected. Three rabbits of Group I
(Nos. 92, 93, 309) died from the effects of caffein; rabbit 309 twenty
minutes after injection, and rabbits Nos. 92 and 93, twenty hours and
two and one-half hours, respectively, after the administration of
caffein. In both of these rabbits symptoms appeared within five minutes
after the injections were made. Rabbits 69 and 70, it will be noticed,
survived the same amount of caffein in proportion to body weight as was
given to the other members of this group. Increased peristalsis and
the distribution of the dose may account for the greater resistance
of rabbit No. 69. The case of rabbit No. 70 is evidently one of
exceptional resistance to caffein, since both the rabbits of Group II
died from the effects of a much smaller dose, namely, 0.15 gram of
caffein per kilo. Moreover, macroscopical examination at the autopsy of
Nos. 307 and 308 failed to show any lesions which might tend to lessen
the resistance to caffein.
That a dose of 0.15 gram per kilo is therefore in all probability the
minimum fatal dose for the rabbit when injected into the peritoneal
cavity appears from the results of the experiments in series C, in
which smaller doses, 0.125 gram of caffein per kilo caused mild
symptoms only, while 0.1 gram per kilo rarely induced any symptoms.
It may be remarked that the rabbits of series C were fed carrots
while rabbits Nos. 307 and 308 received oats. Their resistance to
caffein may be different, but, as was pointed out in the earlier part
of this investigation, diet does not seem to influence the toxicity
of the single dose of caffein. Doses of 150 and of 100 to 125 mg per
kilo, when injected into the peritoneal cavity, may be considered,
respectively, as the minimum fatal and minimum toxic doses for the gray
rabbit. Analysis of the experiments in series D shows much greater
resistance to caffein than in the other rabbits which received it
intraperitoneally. Thus, after the administration of 0.2 gram per kilo
to each of five rabbits, no effect was observed in two cases (Nos.
310, 311), while in two others (Nos. 74, 75) symptoms developed, but
they survived. Only one rabbit, No. 312, died from the effects of this
dose; the autopsy showed the presence of degeneration of the liver and
petechial hemorrhages on the cortex of the kidneys in the case of No.
310, which was probably the cause of death rather than the caffein.
Two decigrams of caffein can not be considered, therefore, the fatal
dose for rabbits. This is further corroborated by the results obtained
in experiments with larger doses. Rabbit 78, which received 257 mg per
kilo, failed to show any symptoms. The same amount in proportion to
body weight in No. 323 caused mild symptoms only, while the rapid death
of rabbit No. 317 after the same dose of caffein may be explained by
the lesion found at autopsy, thus affording additional evidence that
disease may decrease the resistance to caffein. It will be observed
that all the members of this series were young rabbits and, as will
be shown later, young animals of other species are likewise more
resistant to caffein than adult animals. Similar results were obtained
by von Anrep, who observed that atropin is less toxic in young than in
full-grown animals.
Observations were also made on the diuretic effect of caffein when
injected into the peritoneal cavity. The results shown in the following
table indicates the stimulating effect on renal secretion whether
the diet consisted of oats or of carrots. The urine of some rabbits
contained moderate amounts of sugar after from 0.2 to 0.15 gram of
caffein per kilo was given; albumen was observed in one case, but in
none of the others. In rabbit No. 311 albumin was found before the
injection of caffein, but none in the urine which was collected three
hours after caffein was injected.
_Effect of caffein on renal secretion._
-----+--------+---------+-------+--------------------+---------
No. | Weight.| Caffein | Urine.| Time. | Diet.
| |per kilo.| | |
-----+--------+---------+-------+--------------------+---------
|_Grams._| _Gram._ | _cc._ | |
307 | 1,320 | 0.150 | 100 | 4.5 hours | Oats.
308 | 1,305 | .150 | 180 | do. | Do.
295 | 1,205 | .100 | 100 | 2 hours 20 minutes | Carrots.
293 | 1,605 | .100 | 90 | 3 hours | Do.
292 | 1,595 | .100 | 105 | 4 hours | Do.
-----+--------+---------+-------+--------------------+---------
NOTE.--The amount of urine secreted in three hours by control
rabbits, on a carrot diet, varied between 35 and 50 cc, the average
weight of the animals being a little above 1,600 grams. The secretion
of urine on an oat diet was much less for an equal period of time.