PREVITE AND BERRY 



month long acclimatization. Therefore, it is not completely clear 

 whether acclimatization to cold actually enhances the resistance of 

 the mice to endotoxin or merely serves to select more resistant 

 animals for the study. 



Injection of Serratia Marcescens Lipopolysaccharide 



The LDcQ doses of S, marcescens lipopolysaccharide (Difco) 

 were determined to be 38.6 Mg» 408 Mg. and 162.5 Mg at ambient 

 temperatures of 5° C, 25° C, and 35° C respectively. Therefore, 

 both low and high environmental temperature sensitize mice to 

 lipopolysaccharide. 



Timing the Effects of Endotoxin at Different Temperatures 



Mice were given 60-65 Mg of endotoxin (S. marcescens lipopoly- 

 saccharide) placed immediately at 5° C, and at intervals thereafter 

 returned to room temperature. Exposure to cold for 12 hours (46.7 

 per cent survival) sensitizes mice to bacterial lipopolysaccharide 

 almost as completely as continuous exposure (22. 5 per cent survival) 

 (P>0.0 5, Table Va). Survival of 25° C controls (100 per cent) is 

 significantly different from that of 5° C controls (22.5 per cent, 

 P<0.001). It is evident that the response of cold exposed mice to this 

 dose of endotoxin is determined to a great extent within a 12 hour 

 period. Experiments with heat-killed salmonellae (1.6 x 10^ cells, 

 which is more than an LDc^ dose), or with smaller doses of 

 lipopolysaccharide (40 Mg) produced similar results. 



Mice were then given 60-65 Mg of lipopolysaccharide, retained at 

 room temperature, and at intervals thereafter placed in the 5° C 

 room. Survivorship in the groups maintained at 25° C for six hours 

 (70 per cent) and twelve hours (100 per cent) differed significantly 

 from that of mice continuously exposed to 5° C after endotoxin in- 

 jection (22.5 per cent, P<0.001 in both cases; Table Vb). With a 

 lower dose of lipopolysaccharide (40 Mg) similar results were ob- 

 tained. Thus the mouse at normal room temperature (25° C) is able 

 to render non- lethal within a 6-12 hour period a dose of endotoxin 

 that is about 7 5 per cent lethal at an ambient temperature of 5° C. 



224 



