March 17: 3.30 p. m., 3.5 cc 2 per cent caffein (127 mg per kilo) injected into peritoneal cavity; 4.35 p. m., increased irritability present, but not marked; 5.40 p. m., symptoms about the same as before. March 18: 2.30 p. m., condition good; no symptoms. Survived. _Guinea pig 50. Female. Weight, 290 grams. Diet, oats._ April 1: 3.30 p. m., 2 cc 2 per cent caffein (138 mg per kilo) injected into peritoneal cavity; 5.35 p. m., symptoms present; reflexes much increased, but no tetanus. Survived. SERIES B. _Guinea pig 51. Yellow female. Weight, 415 grams._ October 1: 9.50 a. m., 3 cc (144 mg per kilo) 2 per cent caffein injected into peritoneal cavity; 4.30 p. m., no symptoms, although under observation all day. October 3: 2 p. m., alive. _Guinea pig 52. White male. Weight, 450 grams._ October 1: 9.45 a. m., 3.5 cc, 2 per cent caffein (155 mg per kilo), injected into peritoneal cavity; 4.30 p. m., no symptoms developed since injection. October 3: 2 p. m., alive. _Guinea pig 58. Brown and white male. Weight, 490 grams._ October 1: 9.45 a. m., 4 cc, 2 per cent caffein (163 mg per kilo), injected into peritoneal cavity; 4.30 p. m., no symptoms developed since injection. October 3: 2 p. m., alive. October 8: Found dead. _Autopsy_: Congestion of lungs, spleen, liver, kidneys, and small intestines. SERIES C. _Guinea pig 59. Gray and white. Weight, 375 grams. Diet, oats._ October 3: 2 p. m., 3.75 cc (0.2 gram per kilo) injected into peritoneal cavity; 2.15 p. m., reflexes increased but not markedly; 4 p. m., reflexes still more increased; no other symptoms; 5.30 p. m., no symptoms. October 4: 8.50 a. m., guinea pig alive and active. _Guinea pig 58. Brown and white. Weight, 380 grams. Diet, oats._ October 3: 2 p. m., 3.8 cc caffein (0.2 gram per kilo), 2 per cent solution, injected into peritoneal cavity; 2.10 p. m., hind legs extended, then tetanus; attack lasted a few seconds, after which pig raised himself on his legs, but reflexes remained much exaggerated; 4 p. m. to 5.30 p. m., no symptoms of caffein intoxication. October 4: 8.50 a. m., guinea pig alive and active. _Guinea pig 56. Gray and white male. Weight, 440 grams. Diet, oats._ October 1: 11.30 a. m., received 4.6 cc of 2 per cent caffein solution (0.2 gram per kilo) into abdominal cavity; 11.45 a. m., stiffness and rigidity of posterior extremities, reflexes increased; 12.30 p. m., hind legs paralyzed, reflexes increased; 4.35 p. m., no symptoms, guinea pig in good condition. October 3: Still alive in good condition. October 14: Died. _Autopsy_: Anterior lobe of right lung hepatized. Small portion of small intestine edematous. Other organs normal. _Guinea pig 55. White and yellow male. Weight, 690 grams. Diet, oats._