March 1: 10.40 a. m., 6 cc 2 per cent caffein (0.1 gram per kilo) injected into peritoneal cavity; about 2 cc of urine obtained before injecting caffein; 2 p. m. 100 cc urine, bloody in appearance, collected, a moderate quantity of albumen present, no reduction; 3.40 p. m., no symptoms. March 4: 2 p. m., rabbit looks well. _Rabbit 293. Belgian hare, female. Weight, 1,605 grams. Diet, carrots._ March 1: Urine from bladder clear, alkaline; 11.55 a. m., 8 cc 2 per cent caffein (0.1 gram per kilo) injected into peritoneal cavity; 3 p. m., 90 cc urine normal in color collected, no albumen, no reduction; 3.40 p. m., no symptoms. March 4: 1.15 p. m., rabbit looks normal. _Rabbit 292. Belgian hare, male. Weight, 1,595 grams. Diet, carrots._ March 1: 10.10 a. m., 8 cc 2 per cent caffein (0.1 gram per kilo) solution injected into peritoneal cavity; 10.40 a. m., rabbit urinated, reflexes increased, but no other symptoms; 10.50 a. m., no urine obtained from bladder; 2 p. m., 105 cc of clear pale urine collected; no albumen, no reduction; 3.40 p. m., no symptoms. March 4: 2 p. m., rabbit looks well, urine collected, did not contain sugar. _Rabbit 298. Belgian hare, female. Weight, 1,205 grams. Diet, carrots._ March 1: 4.06 p. m., 7.5 cc 2 per cent caffein solution (0.125 gram per kilo) injected into peritoneal cavity, urine obtained from bladder immediately after injection, no albumen, no reduction; 5.30 p. m., reflexes increased, rabbit was able to run around, but became paralyzed soon; 5.40 p. m., rabbit is again able to run around. March 3: 10 a. m., anterior extremities paralyzed, is able to use posterior extremities. March 4: 1 p. m., rabbit looks normal. _Rabbit 223. Belgian hare, male. Weight, 1,165 grams. Diet, carrots._ March 1: 3.50 p. m., urine obtained from bladder clear, amber colored, no albumen, no sugar; 3.52 p. m., 7.5 cc 2 per cent caffein (125 mg per kilo) injected into peritoneal cavity; 5.40 p. m., rabbit makes little attempt to run when put on the floor, weakness of extremities marked. March 4: 1.15 p. m., rabbit normal. SERIES D. 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._