ANTIBODIES TO PNEUMOCOCCUS 419 



refinement of antitoxins, and a similar use of alcohol, have re- 

 ceived wide application in the study of the chemical nature of im- 

 mune substances against Pneumococcus and especially in the quan- 

 tity concentration of antipneumococcic serum. The affinity of the 

 immune bodies for metallic salts also affords a method for the iso- 

 lation of antibody. Now ultracentrifugation and ultrafiltration 

 promise means of separating pneumococcal antibody from the ac- 

 companying components of immune serum. 



THE ESTIMATION OF PROTECTIVE ANTIBODIES 



In the quantitative estimation of the content of protective anti- 

 body in antipneumococcic serum several variables are encountered 

 in the culture, the serum, and the test animal employed. Inasmuch 

 as methods for measuring the therapeutic potency of antipneumo- 

 coccic serum will be discussed in the chapter dealing with serum 

 production, brief mention may be made at this point of some of the 

 factors which may influence the accuracy of the determination. 

 Enlows 366 pointed out the necessity of using cultures in the phase 

 of active growth or in the early stationary phase in order to avoid 

 lag on transfer. The hydrogen ion concentration of the medium in 

 which the pneumococci are grown should be such as to ensure the 

 presence of cocci at the height of vitality. The virulence of the 

 culture should be maintained at a high level. Felton 402 standard- 

 ized the infecting dose of culture by plate counts and employed a 

 dilution of culture representing 500,000 fatal doses of organisms. 



Felton (1926) 399 discovered in antipneumococcic serums for 

 Types I, II, and III, a substance that was lethal for mice. Later, 

 Felton and Bailey 419 pointed out that from immune serum precipi- 

 table residues could be isolated that had an antagonistic action on 

 the neutralization of protective antibody by capsular polysaccha- 

 ride. Furthermore, the amount of soluble specific substance oper- 

 ated to cause a zonal effect in the estimation of protective action. 



The mouse, on account of race, age, weight, and physical condi- 

 tion, presents an array of variable factors in the response to the 



