Bactericidal Action on Pneumococcus 225 



centrifugation the cells were suspended in gelatin salt solution 

 and a count of the white blood cells made. A second washing 

 with gelatin Locke's solution was done and the cells finally sus- 

 pended in this solution in known concentration. Solutions for 

 washing and suspending leucocytes were adjusted to P H 7.2-7.6. 

 In addition to the leucocytes washed red blood cells were added 

 as indicators of pneumococcus growth. 



Results 



It was found that pneumococci seeded into 0.3 c.c. cat's serum 

 plus 0.1 c.c. leucocyte suspension containing 50,000 white blood 

 cells per c.mm. (the equivalent number of white blood cells 

 contained in 0.5 c.c. of blood with a count of 10,000 per 

 c.mm.) failed to grow in numbers less than 0.001 c.c, or at most 

 0.0001 c.c, whereas the control tubes containing serum alone 

 showed growth with 0.0000001 c.c of organisms. The tubes 

 were allowed to incubate for varying lengths of time, from 24- 

 72 hours before microscopic examination was made. The con- 

 tents of those tubes showing no growth were transferred into 1 

 per cent, dextrose blood broth P H 8.0 and rabbit blood agar plates 

 P H 7.8 in order to determine the presence or absence of living 

 pneumococci. Organisms could not be recovered from the tubes 

 which failed to show growth. The media used for these tests had 

 been determined beforehand to be highly favorable for the growth 

 of very small numbers of pneumococci. Further experiments 

 were made in which mice were employed as a culture media. The 

 results of these tests showed that after 24 hours sojourn in the 

 cat serum-leucocyte mixture as much as 10,000 times the killing 

 dose of pneumococci failed to kill the test mice. Tests carried 

 out on the dog serum and leucocytes gave similar results. On the 

 other hand, the serum-leucocyte mixtures of susceptible animals, 

 the rabbit and guinea pig, showed no growth inhibiting action 

 against pneumococci. Even such a small number of organisms 

 as 0.0000001 c.c. of the standard suspension grew readily in the 

 blood elements of these animals. 



The results of the above experiments seem to warrant the con- 

 clusion that with the technique employed, a mixture of serum and 

 leucocytes from resistant animals can be shown to exert not only 

 a growth inhibiting but also a bactericidal action on the pneu- 

 mococcus. 



