SPECIFIC AND NONSPECIFIC RESISTANCE 



serted the probe uniformly 2 cm into the rectum, whereas Walker 

 and Boring inserted the probe only 1 cm. 



In spite of the differences in results of these two groups with 

 regard to the increase or decrease inthebody temperature of mice 

 as a result of cold exposure, the degree of change was not outside 

 the range compatible for optimal growth and development of the 

 organisms employed for parenteral challenge. Therefore, we felt 

 that any changes in susceptibility or resistance to disease could 

 now be ascribed to factors other than that related to core tempera- 

 ture per se. 



The fact that the K. pneumoniae isolated from animals maintained 

 at 2° C did not vary in virulence as compared to the same organism 

 isolated from mice maintained at 21° C led us to conclude that this 

 organism could be used with confidence as a challenge agent to ob- 

 tain the desired mortality ratios when given to mice kept at 21° C or 

 2° C. The observation that the isolate from mice maintained at 2° 

 would grow equally well at incubation temperatures of 37° C or 32° C 

 requiring only one- half the oxygen used at 32° C suggests that these 

 organisms are more metabolically efficient in contrast to organisms 

 isolated from animals maintained at 21° C and grown under the same 

 conditions. This deserves further investigation. 



In general, specific immunization protected significantly, whereas 

 nonspecific substances which have been used to increase resistance 

 (zymosan and endotoxin) did not afford the same degree of pro- 

 tection when the challenged animals were exposed to 2° C either as 

 acclimatized or unacclimatized mice. This was true whether the 

 challenge agent was K, pneumoniae , S, aureus, or the B-1 strain 

 of Coxsackie virus. 



The increased resistance afforded by immunization was maximal 

 when mice were exposed to low ambient temperatures in groups. 

 Mice that were caged individually did not fare so well. Since the core 

 temperatures of mice caged individually or in groups equilibrated 

 within 24 hours of low temperature exposure, one cannot validly 

 state that loss of body heat is a contributing factor to lessened re- 

 sistance. However, it might be hj^jothesized that the metabolic rate 

 of individually caged mice is increased over that of grouped animals, 



191 



