MIRAGLIA AND BERRY 



to maintain normothermia when kept at 5° C for 10 to 15 days has 

 been reported previously byBischoff (1942). Nevertheless, moribund 

 animals in the cold do become markedly hypothermic, as they do 

 during the last hours of life at room temperature when suffering 

 from salmonellosis. 



The data to be presented confirm and extend those of Previte and 

 Berry (1962) who demonstrated an increase in host susceptibility to 

 infection with Salmonella typhimur ium when a strain of low virulence 

 but not one of high virulence was used in mice continuously exposed 

 to a low ambient temperature. In addition, and perhaps of even 

 greater importance, is the observation that a second invading or- 

 ganism, a coagulase- negative staphylococcus, presumably from the 

 environment or from the mouse itself, becomes established in tis- 

 sues of the host already stressed by cold and the experimental 

 salmonellosis. It has longbeenbelieved that primary infections pre- 

 dispose an animal to secondary invasion but, heretofore, experi- 

 mental evidence for this has not been clear. To the authors' know- 

 ledge, this is the first description of a situation which permits 

 consistent prediction of the incidence of secondary infection. 



MATERIALS AND METHODS 



Animals. CFj female mice (Carworth Farms, New York City, 

 New York) weighing 20 to 22gmwereused in all experiments. They 

 were housed in plexiglass cages which were divided into 10 equal 

 compartments per cage. Each compartment measured 3.5 x 7.5 x 

 9.0 cm. No bedding was used, and mice were housed individually to 

 prevent huddling. The open tops and bottoms of the plexiglass en- 

 closures were covered with 3/8 inch mesh hardware cloth. All com- 

 pletely assembled cages were placed on wire meshto keep the ani- 

 mals free from excessive moisture and excreta. Water and pathogen- 

 free mouse food (Dietrich and Gambrill, Frederick, Maryland) were 

 available at all times. 



Animal Rooms . Two animalrooms were used; one was maintained 



274 



