BIOLOGY OF PNEUMOCOCCUS 63 



For killing cultures to be used as antigens for the production of 

 active immunity 0.5 per cent phenol and 0.3 per cent formalin are 

 commonly used. Sodium ricinoleate was first used for this purpose 

 by Larson and Nelson, 791 because of its rapid lethal effect on pneu- 

 mococci and the absence of any impairing action on the antige- 

 nicity of the treated cells. Barnes and Clarke 81 determined that 

 sodium ricinoleate and sodium oleate were pneumococcidal in con- 

 centrations of 0.04 and 0.004 per cent respectively, which, in con- 

 junction with Lamar's results on the action of sodium lanolate, 

 give us definite figures for these soaps. 



In discussing the effect of various chemical substances on the vi- 

 tality of Pneumococcus, mention may be made of the method devel- 

 oped by Schnabel 1238 " 9 for measuring such effects. Based on the re- 

 ducing power of pneumococci, he determined the ability of the 

 organism in contact with varying strengths of the test chemicals 

 to produce significant color changes in methylene blue, litmus, neu- 

 tral red, indigo blue, and other dyes. Since the reducing power of 

 pneumococci is a variable one, this factor must be carefully con- 

 trolled by proper observance of time, temperature, and hydrogen 

 ion concentration. The method enabled Schnabel to study both the 

 inhibiting and the sensitizing action of quinine, optochin, mercuric 

 chloride, formaldehyde, phenol, and silver nitrate on Pneumococ- 

 cus. The method holds possibilities for the study of drug-fastness 

 of the coccus and Schnabel claimed that by the use of this tech- 

 nique he could determine the presence of optochin in a 1 to 1,000,- 

 000 dilution and that it can be applied to the quantitative meas- 

 urement of the amounts of analogous substances in solution. 



The discovery by Morgenroth and Levy 926 that quinine and some 

 of its derivatives, especially optochin, possess bactericidal powers 

 for Pneumococcus, both in vitro and in vivo, has led to investiga- 

 tions on the therapeutic effect of this class of substances on pneu- 

 mococcal infection. The results of the studies will be discussed in 

 the chapter on Chemotherapy. 



To summarize our knowledge of the bactericidal action of vari- 



