The object of these experiments was to determine the minimum fatal dose of caffein in the two varieties of rabbits, the white and the gray. All of the animals selected were approximately of the same weight. _Rabbit 239. Belgian hare, male. Weight, 935 grams. Diet, oats._ November 19: 4 p. m., 17 cc 2 per cent caffein (363 mg per kilo) administered by mouth, followed by 10 cc of 0.9 per cent salt solution. November 20: Urine examined, no sugar found, no symptom noticed at any time after injection. _Rabbit 254. Belgian hare, female. Weight, 975 grams. Diet, oats._ November 19: 4.05 p. m., 18 cc 2 per cent caffein (369 mg per kilo) administered by mouth, followed by 10 cc of 0.9 per cent salt solution. November 20: 9 a. m., rabbit found dead. _Rabbit 267. White. Weight, 1,050 grams. Diet, oats._ November 23: 12.10 p. m., 18 cc 2 per cent caffein (342 mg per kilo) given by mouth, followed by 18 cc salt solution; 1 p. m., increased reflexes, tremors marked but no tetanus; 1.05 p. m., rabbit stretched on abdomen, posterior extremities in extended position and paralyzed, soon after clonic spasms set in, which recurred about every minute; 1.14 p. m., tetanus and death. _Autopsy_: Liver showed fatty degeneration; slight inflammation of stomach and intestines; other organs normal. _Rabbit 268. White. Weight 1,100 grams. Diet, oats._ November 23: 20 cc 2 per cent caffein (363 mg per kilo) administered by mouth, followed by 20 cc salt solution; 1.15 p. m., somewhat hypersensitive; 4.30 p. m., tremors fairly marked, no urine passed, about 2 cc of bloody looking urine obtained from bladder, which contained albumen and a considerable amount of glycogen; rabbit died. _Rabbit 419, Belgian hare, male. Weight, 1,600 grams. Diet, oats._ September 26: 10 a. m., 28 cc 2 per cent caffein (350 mg per kilo) given by mouth; reflexes increased at 4 p. m.; 6 p. m., reflexes still increased, no other symptoms. September 27: 9 a. m., found dead. _Autopsy_: Lungs, liver, and kidneys congested; other organs normal. _Rabbit 420. Belgian hare, male. Weight, 1,250 grams. Diet, oats._ September 26: 10 a. m., 22 cc 2 per cent caffein (352 mg per kilo) given by mouth; 11.35 a. m., convulsions; 12 noon, found dead. _Autopsy_: Liver showed very extensive coccidiosis; no other lesions. _Rabbit 421. Belgian hare, male. Weight, 1,485 grams. Diet, oats._ September 26: 10 a. m., 26 cc 2 per cent caffein (351 mg per kilo) administered by mouth; 4 p. m., reflexes increased; 6 p. m., reflexes as before, no tetanus observed. September 27: 9 a. m., rabbit found dead. _Autopsy_: Congestion of lungs and kidneys; liver congested and slightly fatty. _Rabbit 424. White, male. Weight, 1,295 grams. Diet, oats._ September 26: 2 p. m., 19 cc 2 per cent caffein (293 mg per kilo) administered by mouth; 4 p. m., reflexes increased, no other symptoms; 6 p. m., no change since 4 p. m.