ADMINISTRATION BY MOUTH. All the guinea pigs in these experiments were kept on a diet of hay and oats and were of large size. The tests were made with different doses of caffein in order to determine the limits of toxicity when the drug was administered by mouth. _Guinea pig 129. White and black male. Weight, 855 grams. Diet, oats and hay._ June 6: 2.20 p. m., 12 cc of 2 per cent caffein (0.28 gram per kilo) by mouth; 3 p. m., reflexes increased; 5 p. m., reflexes still more increased; no other symptoms. June 7: 9 a. m., found dead; guinea pig passed 75 cc urine, which was almost colorless. _Autopsy_: Heart and blood vessels injected; lungs congested; small intestines congested; other organs apparently normal. _Guinea pig 130. Black and brown male. Weight, 800 grams. Diet, oats and hay._ June 6: 2.30 p. m., 12 cc of 2 per cent caffein (0.3 gram per kilo) administered by mouth; 3 p. m., reflexes increased; 5 p. m., increase of reflexes greater than at 3 p. m. June 7: 9 a. m., found dead; only a few cubic centimeters of urine passed since 4 p. m. _Autopsy_: Heart and blood vessels injected; lungs congested; small intestines congested slightly. _Guinea pig 181. White and yellow male. Weight, 860 grams. Diet, oats and hay._ June 6: 2.40 p. m., 12 cc 2 per cent caffein administered by mouth; 3 p. m., reflexes increased; 5 p. m., reflexes still more marked. June 7: 9 a. m., found dead, pig passed about 5 cc urine since 4 p. m. of previous day. _Autopsy_: Same as in No. 130. _Guinea pig 136. White and black male. Weight, 1,000 grams. Diet, oats and hay._ June 9: 4 p. m., 7.5 cc 2 per cent caffein solution injected subcutaneously into the back; 4.50 p. m., reflexes increased. June 10: 9.30 a. m., more sensitive than normal guinea pigs, but reflexes not quite so marked as at 5 p. m. previous day, about 15 cc urine passed since caffein was injected, reduction of Fehling's solution considerable, no albumin. June 13: Alive and in good condition. Appetite good. (NOTE.--Parallel test with urine from two guinea pigs which did not receive caffein failed to show reduction of Fehling's solution.) _Guinea pig 137. White and brown male. Weight, 925 grams. Diet, oats and hay._ June 9: 4 p. m., 7 cc 2 per cent solution caffein injected subcutaneously; 4.50 p. m., reflexes increased. June 10: Reflexes less marked than at 5 p. m. previous day, but is more sensitive than normal guinea pig, about 10 cc urine passed since injection of caffein, moderate amount of reduction of Fehling's solution. June 13: Guinea pig alive, appetite good, condition good. June 16: 9 a. m., found dead. _Guinea pig 135. White and black male. Weight, 955 grams. Diet, hay and oats._ June 9: 3 p. m., 7.5 cc 2 per cent caffein solution given by mouth through stomach tube; 4.50 p. m., reflexes increased.