That the resistance to drugs may vary according to the age of the subject has been maintained by a number of pharmacologists. According to Guinard,(30) young dogs, rabbits, and guinea pigs are very susceptible to morphin, resembling children in this regard.[E] The minimum fatal dose for these animals is about one-third less than for the adult. This is not true, however, for the young of other species. Cats under 15 days of age tolerate twice the toxic dose of morphin for the adult cat. Young beeves and goats are likewise more resistant to this alkaloid than adults. On the other hand, according to Livon,(54) young guinea pigs are more sensitive to alkaloids than adults. The toxicity of caffein, as shown in the present investigation, was found to be less in the young than in the adult. In dogs the young subjects are in some instances almost twice as resistant as adults. The difference was found to be less in cats and rabbits than in dogs, but it was quite marked. [E] A case of accidental poisoning reported recently by Wichura (Münich. Méd. Woch., 1911, No. 30, p. 1618) throws some doubt on the accepted view that the susceptibility of young children to morphin is greater than that of adults. Wichura also found that the therapeutic doses of codein preparations ordinarily recommended for children in pleuritic cough are not effective in this condition. The effect of season on the toxicity of drugs has been discussed in the section on the experiments on guinea pigs, which were more resistant to caffein in the fall than in February and March. The effect of season seems to vary with the animal, but it may also differ with the substance employed. In Noe's(65) studies on this subject cantharidin was found to be more toxic for the hedgehog in November than in July. The effect of season was different for morphin, as it was observed that the resistance of the hedgehog was greater at the end of the summer than earlier in the season. The relation of diet to toxicity of drugs has been studied by Hunt.(39) His experiments indicate that this is an important factor in the resistance to acetonitril. The studies here reported on the effect of diet on toxicity of caffein in rabbits were confined to experiments with oats and carrots and do not show any modification of the resistance to caffein. The question of diet in chronic intoxication in dogs, however, suggests that in these animals diet may affect the toxicity of caffein, although the data on this subject are far from satisfactory. There is nevertheless sufficient evidence to suggest that a high protein diet for the adult dog tends to greater resistance of the animal to caffein and similarly the growing dog tolerates larger quantities of caffein on a milk diet than on a diet of meat.