Parisot(68) (1890) made a study of the toxicity of caffein on different species of animals. Unlike most of his predecessors, however, he reported, at least in some cases, the weight of the animals on which he worked. After the subcutaneous and intramuscular injections of from 5 to 20 mg of caffein into _Rana temporaria_ weighing from 14 to 16 grams, he noticed increased irritability at first; later, a loss of reflexes, inability to use the muscles, complete muscular rigidity resembling rigor mortis, and also cessation of heart action. The effect of caffein produced in the green frog was analogous to that observed in strychnin poisoning. Parisot found, however, that muscular rigidity developed, although very gradually, also in the green frog, but it set in much later than in frogs of the other species and without superseding the clonic convulsions. According to Parisot, the muscular rigidity after caffein persists after the destruction of the brain and spinal cord, thus showing that it is not of nervous origin. He further emphasized the difference in the behavior of these two species of frogs toward caffein by stating that he never observed tetanic convulsions in the red frog. His experiments also indicate that the green frog is more resistant to caffein than _Rana temporaria_, as the same doses which are fatal for the latter were only toxic for _Rana esculenta_. The number of experiments, however, is too few to justify a positive conclusion on this point. Parisot also made some experiments on turtles. The results he obtained show that caffein is at least as toxic for these animals as for the frogs he experimented upon, 0.33 gram per kilo (carapace not included in weight) having proved fatal within 24 hours. Two experiments on one pigeon were also reported by the same observer; two doses of 0.06 gram per kilo given at an interval of four hours caused mental depression and muscular rigidity, but the pigeon survived. Experiments with caffein on the human subject made by Parisot showed that man is far more susceptible to this substance than the other animals he investigated. After the ingestion of 0.3 gram of caffein symptoms of intoxication pointing to cerebral disturbance appeared, which became more marked when the size of the doses was increased.