Since the experiments of Series A, which were intended as preliminary tests, have shown that 0.3 gram of caffein per kilo when introduced into the peritoneal cavity is rapidly absorbed and is fatal, much smaller doses were employed in subsequent trials with the drug. This is shown in series B, which may be divided into two groups. Group I, consisting of rabbits 69, 70, 92, 93, and 309, which received 0.2 gram of caffein per kilo, and Group II, Nos. 307 and 308, into which 0.15 gram of caffein per kilo was injected. Three rabbits of Group I (Nos. 92, 93, 309) died from the effects of caffein; rabbit 309 twenty minutes after injection, and rabbits Nos. 92 and 93, twenty hours and two and one-half hours, respectively, after the administration of caffein. In both of these rabbits symptoms appeared within five minutes after the injections were made. Rabbits 69 and 70, it will be noticed, survived the same amount of caffein in proportion to body weight as was given to the other members of this group. Increased peristalsis and the distribution of the dose may account for the greater resistance of rabbit No. 69. The case of rabbit No. 70 is evidently one of exceptional resistance to caffein, since both the rabbits of Group II died from the effects of a much smaller dose, namely, 0.15 gram of caffein per kilo. Moreover, macroscopical examination at the autopsy of Nos. 307 and 308 failed to show any lesions which might tend to lessen the resistance to caffein. That a dose of 0.15 gram per kilo is therefore in all probability the minimum fatal dose for the rabbit when injected into the peritoneal cavity appears from the results of the experiments in series C, in which smaller doses, 0.125 gram of caffein per kilo caused mild symptoms only, while 0.1 gram per kilo rarely induced any symptoms. It may be remarked that the rabbits of series C were fed carrots while rabbits Nos. 307 and 308 received oats. Their resistance to caffein may be different, but, as was pointed out in the earlier part of this investigation, diet does not seem to influence the toxicity of the single dose of caffein. Doses of 150 and of 100 to 125 mg per kilo, when injected into the peritoneal cavity, may be considered, respectively, as the minimum fatal and minimum toxic doses for the gray rabbit. Analysis of the experiments in series D shows much greater resistance to caffein than in the other rabbits which received it intraperitoneally. Thus, after the administration of 0.2 gram per kilo to each of five rabbits, no effect was observed in two cases (Nos. 310, 311), while in two others (Nos. 74, 75) symptoms developed, but they survived. Only one rabbit, No. 312, died from the effects of this dose; the autopsy showed the presence of degeneration of the liver and petechial hemorrhages on the cortex of the kidneys in the case of No. 310, which was probably the cause of death rather than the caffein.