Examination of the results obtained in the experiments of series C shows that young and growing dogs tolerate large amounts of caffein. In four subjects of this series, Nos. 1, 2, 3, and 6, no effect was observed when moderately large amounts (160 to 200 mg per kilo of caffein) were fed. Symptoms were noticed only when these amounts of caffein were increased from 50 to 60 per cent. The other two dogs, Nos. 4 and 5, of this series were less resistant, however, to caffein, as 0.16 gram of the drug per kilo induced well-marked symptoms. Since these were fed meat, while Nos. 1, 2, and 3 received milk, the difference in toxicity may be due to the diet employed, but No. 6, which likewise received a meat diet, failed to show the effects of caffein when 200 mg per kilo were fed. On the other hand, it should be noticed that No. 1 died after receiving 360 mg per kilo, No. 2 survived a dose of 334 mg, while No. 3 died after a dose of 322 mg per kilo of caffein. The fatal doses for Nos. 4, 5, and 6 were 287, 335, and 300 mg per kilo, respectively. Although the differences are too small to justify any definite conclusion regarding the effect of a milk diet or of a meat diet on the toxicity of caffein, the results nevertheless suggest a reasonable possibility that caffein is more toxic to young dogs when on an exclusively meat diet than when fed milk. It is perfectly evident, however, that the resistance to caffein in either case is very great, almost twice that of adult subjects. As shown in series A and B, 125 to 175 mg per kilo proved fatal to all but two animals in these experiments, while symptoms of toxicity appeared after much smaller doses. In other respects the behavior of young dogs toward caffein was the same as that of the adult. In neither case was cumulation nor tolerance observed under the conditions of these experiments. The findings at autopsy were likewise similar, as gastro-enteritis was the chief lesion observed on macroscopic examination. It might be mentioned, however, in this connection, that the symptoms of caffein intoxication in young dogs often presented marked differences from those observed in those of more advanced age. The resemblance of the effects of caffein in young puppies and in rabbits was very striking. In both, the tonic with clonic convulsions were observed after a sufficient quantity of caffein was administered. In the dogs which were fully grown a large dose of caffein was usually followed by tonic convulsions and almost instantaneous death.