SECONDARY BACTERIAL INFECTION IN MICE 



at 25° C ± 2° C, the other at 5° C i 1° C. An automatic lighting 

 system provided 12 hours of light for each 24 hour period. The mice 

 were kept continuously in the appropriate room for the entire ex- 

 perimental period. Humidity was not controlled but results were re- 

 producible at different seasons of the year when humidity is known 

 to vary. 



Inoculum. Two strains of Salmonella typhi murium were used, the 

 highly virulent SR-11 and the relatively avirulent RIA. Both strains 

 were cultivated in brain-heart infusion broth (Difco) for 16 hours at 

 37° C. Decimal dilutions of the cultures were prepared with pyrogen- 

 free saline (Baxter Laboratories, Morton Grove, Illinois) and were 

 plated in triplicate on both nutrient and SS agar plates (Difco) to e- 

 numerate the colonies and to insure the uniformity of the culture. 

 Inoculations consisting of the appropriatenumber of organisms con- 

 tained in 0,5 ml of saline were administered by the intraperitoneal 

 route, 



Oygan culture technique . Tissues (heart, lung, kidney, spleen and 

 liver) selected for bacterial culture were excised by aseptic tech- 

 nique from mice immediately after death. Samples were cultured on 

 appropriate media for identification of microflora, using the organ 

 print method. Nasal cultures were also desired, but owing to the 

 obvious difficulties in attempting to obtain inocula from the naso- 

 pharynx, only the external nares of the animals were cultured by 

 the imprint method on appropriate medium for staphylococci. 



Stool culture technique . Stool cultures were made, where indi- 

 cated, by placing into the appropriate medium a single fecal pellet 

 obtained on a sterile swab at the time of defecation. To culture for 

 staphylococci, a pellet was incubated at 37° C in brain-heart in- 

 fusion broth containing 7 per cent sodium chloride for 16 to 18 hours 

 before streaking on Staphylococcus 110 medium (Difco) . To culture 

 for salmonellae, a second specimen was similarly incubated in 

 selenite broth (Difco) before streaking on SS agar. 



Coagulase test. The coagulase test was conducted in Was sermann 

 tubes using 0.5 ml of reconstituted coagulase plasma (Difco) to which 

 was added two drops of a 16 hour brain- heart infusion culture of the 

 staphylococcus under test. Tubes were read after three hours incu- 



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