_Rabbit 428. Belgian hare, gray, male. Weight, 1,650 grams._ October 5: 4 p. m., 14.8 cc 2 per cent caffein (0.18 gram per kilo) injected into the lumbar muscles. October 6: Found dead. _Rabbit 429. Belgian hare, male. Weight, 1,340 grams._ October 5: 4 p. m., 13.5 cc 2 per cent caffein (0.2 gram per kilo) injected into lumbar muscles. October 8: Rabbit found dead. SERIES D. Further experiments making injections into both the lumbar and the gluteal muscles, were made in this series. _Rabbit 577. Gray male. Weight, 1,380 grams._ February 14: 3 p. m. 14 cc 2 per cent caffein injected into the gluteal muscles of the right side; 3.10 p. m., restless, jumped off the table and walked about, reflexes increased; 3.45 p. m., passed 30 cc clear, straw-colored urine; 4.45 p. m., allowed to walk about, ran across the room, about 20 feet, looked tired, stretched himself out on the floor, then raised himself and walked about showing no disturbance of gait. February 15: 9 a. m., found dead. _Rabbit 578. Gray, female. Weight, 1,670 grams._ February 14: 3.05 p. m., 18 cc 2 per cent caffein solution injected into the gluteal muscles of the right side; 3.15 reflexes increased, but not restless; 5 p. m., allowed to walk about, no symptoms observed. February 15: Found dead. _Rabbit 579. White and gray, male. Weight, 1,490 grams._ February 14: 3.15 p. m., 15 cc 2 per cent caffein solution injected into the gluteal muscles of the right side; put in cage; 3.30 p. m., reflexes increased; 5 p. m., taken out of cage and allowed to walk across the room, no special symptoms noticed. February 23: Still alive. _Rabbit 580. Gray male. Weight, 1,510 grams._ February 14: 3.35 p. m., 15 cc 2 per cent caffein solution injected into lumbar muscles. February 23: Still alive, in good condition. _Rabbit 581. Gray female. Weight, 1,680 grams._ February 14: 3.45 p. m., 17 cc 2 per cent caffein solution injected into the lumbar muscles of the right side; 4 p. m., reflexes increased; 4.15 p. m., jumped off the table and had wild convulsions, became very restless, walked about the laboratory; 4.25 p. m., had convulsions occasionally; 4.30 p. m., extremities extended and quite rigid; 4.35 p. m., convulsions and death. _Rabbit 582. Gray male. Weight, 1,870 grams._ February 14: 4.15 p. m., 18 cc 2 per cent caffein solution injected into the lumbar muscles of right side; 5 p. m., reflexes increased; walked about in the room, then rested; 5.15 p. m., had short spasm when handled. February 23: Alive; good condition. The data presented in these experiments show that the toxicity of caffein when injected into the muscles of the lumbar regions is the same as when injected into the gluteal muscles. The rabbits of series A received approximately 0.2 gram caffein per kilo and two died as a result of this treatment. The other two survived but symptoms of caffein intoxication were observed.