VIRULENCE AND BACTERIAL INFECTION 



Injections of bacteria derived from 17 hour brain-heart infusion 

 cultures, and lipopolysaccharide derived from Serratia marcescens 

 (Difco), as well as heat- killed Salmonella typhi murium , were 

 suspended in 0.5 ml of non-pyrogenic saline (Baxter's) and ad- 

 ministered at the start of each experiment. All injections were 

 given intraperitoneally other than staphylococci which were given 

 intravenously via the tail vein of the mouse, A viable count of 10^ 

 cells per ml based on numerous experimental determinations was 

 assumed for the undiluted cultures. Staphylococcal toxins were 

 obtained as sterile filtrates of the contents of diffusion chambers 

 which were constructed with Viscose dialyzing membranes. Staphyl - 

 ococcus aureus, Giorgio, had been grown inside the chambers for 

 10 to 14 days after implantation in the peritoneal cavities of mice. 

 This technique is described in detail by Houser and Berry (1961). 

 Mice were injected intravenously with 0.1 ml of a 1:32 dilution of 

 the filtrate and placed immediately at 5° C or 25° C, The material 

 was supplied by Mr. Enoch D, Houser. 



Rectal temperatures were determined by inserting a thermistor 

 probe approximately 21 mm into the rectum of mice for twenty 

 seconds. The temperature was read from a telethermometer 

 (Yellow Springs Instrument Company, Yellow Springs, Ohio) to 

 which the probe was connected. A mercury thermometer was used 

 to calibrate the instrument. 



Five mg of cortisone was administered subcutaneously as a sus- 

 pension of cortisone acetate (Nutritional Biochemicals, Cleveland) 

 in 0.5 ml of non-pyrogenic isotonic saline solution. The suspension, 

 stabilized with a drop of Tween 80 detergent was prepared in a 

 glass homogenizer with teflon pestle and used immediately there- 

 after. Adrenocorticotrophic hormone, ACTH, (Armour Labora- 

 tories, Chicago) was injected as a gelatin suspension (Acthar Gel) 

 containing two units per 0.05 ml. 



The significance of differences in survival due to experimental 

 treatments was determined by the chi- square test using Yate's 

 corrected formula (Croxton, 1959) and that for rectal temperature 

 measurements was determined by the rank order test (White, 1952), 

 For some treatments mean survival times were calculated, in- 

 cluding only the mice that died, LD dosages were determined 



uO 

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