MIRAGLIA AND BERRY 



bation at 37° C. 



Miscellaneous . In lieu of drinking water, 0.0 IN hydrochloric acid 

 (pH 2.0) was given to mice to rid the gut of staphylococci. This is a 

 modification of the method of Schaedler and Dubos (1962), The ab- 

 sence of the organisms was confirmed by stool culture. Where re- 

 colonization of the intestine with a specific strain (in this case 

 Staphylococcus aureus, strain Giorgio) was desired, the hydrochloric 

 acid treatment was terminated before feedingthe mouse for a period 

 of 12 hours the desired microorganism as a contaminant in the ration. 



RESULTS 



Determination of LD ty). TheLDso for animals infected with strain 

 RIA and maintained at 50Cand25°C was determined by the method 

 of Reed and Muench (1938). This was found to be 4.1 x 10^ cells per 

 mouse at 25° C and 3.8 x 10^ cells per mouse at 5° C, as shown in 

 Table I. The LD5Q for the highly virulent SR- 11 strain was less than 

 seven cells per mouse at room temperature, hence a temperature 

 effect was not demonstrable. All observations were terminated after 

 a period of 14 days. 



The space limitation imposed on mice housed in the compart- 

 mented cages did not alter the LD50 dose of the RIA strain of 

 S. typhimurium at 25° C. This was true also for the LD50 dose of 

 crude bacterial endotoxin administered by intraperitoneal injection. 

 Neither crowding nor the psychological effects of isolation under a 

 situation where neighboring mice were visible through the clear 

 plexiglass made any measurable difference in these animals coni- 

 pared to those normally housed. 



The same type of control experiment could notbe conducted, how- 

 ever, at 5° C since animals permitted to huddle are not as severely 

 stressed by cold as those kept in isolation. This can be seen from 

 the following experiment. Animals were housed 10 per cage (10 x 7 x 

 6 1/2 inches) with pine shavings as bedding and without restriction 



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