SPECIFIC AND NONSPECIFIC RESISTANCE 



mortality of grouped or &ingly-caged normal animals was ob- 

 served. Immunization protected the counterpart groups to the 

 same extent. It can be concluded from these results that the 

 mice chronically exposed to an ambient temperature of 2° C 

 were able to form agglutinin antibody and that the immuniza- 

 tion procedure offered significant protection against the challenge 

 organisms. In contrast, the normal mice chronically exposed 

 to 2° C were adversely affected by K. pneumoniae ; that is, 

 smaller numbers of organisms caused increased mortality whether 

 the animals were grouped or caged individually. 



Effect of Acute and Chronic Low Temperature Stress on Survival 

 of Mice Challenged with Staphylococcus Aureus 



Four strains of S, aureus were tested for their virulence for 

 mice via the IP route in order to determine which would be the 

 most suitable for subsequent studies. The Fritchie strain was 



n 



found to be the most virulent. The LDcq was 25x10 organisms 

 with 95 per cent confidence limits of 13 x 10^ to 47 x 10^. Deaths 

 of animals challenged with one LD_^ of the Fritchie strain usually 

 occurred within 5 to 10 hours after challenge; however, the 

 experiments were not terminated until 7 to 10 days had elapsed. 



In the acute exposure experiments, mice were immunized at 

 21° C, Immediately following the IP challenge, the mice were 

 kept either at 21° C or transferred to 2° C. The mice that were 

 transferred to the low ambient temperature were caged either 

 in groups of 10 animals or as individuals. The results of a typical 

 experiment in Table IV show that a dose-response effect from 

 S. aureus , Fritchie strain, is obtainable whether mice are ex- 

 posed to the cold environment or kept at room temperature. 

 Note that immunization is effective in protecting the challenged 

 mice kept at 21° C and in groups at 2° C; in contrast, immuni- 

 zation did not afford protection to mice caged individually. Al- 

 though not listed in the table, non- challenged cold stress con- 

 trol mice caged individually did not die during the experimental 

 period (mortality ratio, O/lO), 



Mice that were chronically exposed to low ambient temperatures 



171 



