approved.

ii Acute exposure of mice to an environmental temperature of either 50 C or 370 C reduced the LD of a crude Serratia marcescens endotoxin from a high of2300 ag in mice housed at 30C C to an amount less than 40 Vg. At 15 C or 320 C, the LD was, respectively, 880 jig and 550 jig, while at 25 ° C it was 200 Mg. Control animals placed it each of 'hese tempera-tures were able to maintain normothermia except for those at the high and low extremes where they became slightly hyper-thermic and hypothermic. Following an injection of either twice the LD or a dose oi 1000 jg, the thermoregulatory50 0 ability was upset at all temperatures except 30 G. Mice at temperatures below 30 C became progressively more nypo-thermic as the environment was increasingly cold and vice vers