PRODUCTION OF ANTIPNEUMOCOCCIC SERUM 531 



the demonstration of antitoxic properties in immune serum so pro- 

 duced. 



The methods of choice in devitalizing pneumococcal vaccines ap- 

 pear to have become reduced, in recent years, to treatment either 

 with heat or with formalin. For immunizing horses, Savino, Ne- 

 grete, and Acuna (1931 ) 1221 added 0.2 per cent formalin to cul- 

 tures and then centrifuged out the organisms. Pico and Negrete 1089 

 added 0.5 per cent of formalin to suspensions to be used for the 

 same purpose, and claimed that the preparations retained their 

 antigenic power over a long period of time. Tao 1380 compared the 

 immune response of rabbits and mice injected with heat-killed vac- 

 cines and suspensions of pneumococci killed by exposure to 0.3 per 

 cent formalin for eight hours. He reported that formalinized vac- 

 cines stimulated the production of specific antibodies quite as well 

 if not better than did heated suspensions, but it was observed that 

 the immunity developed in the animal body under the stimulus 

 from formalin-treated vaccine appeared somewhat later than that 

 from heated vaccine. The latter observation was confirmed by the 

 work of Barnes and White (1934) 86 during studies on the com- 

 parative antigenicity of heat-killed and formalinized vaccines in 

 rabbits and horses but, contrary to Tao's observations, vaccines 

 killed by one-hour exposure to 56° were at least as effective, if not 

 more so, than the formalinized suspensions. In addition, heat-killed 

 vaccines appeared to be somewhat less toxic than those treated 

 with formalin. 



The amount of formalin used by different workers in preparing 

 pneumococcal vaccines has varied. In this connection, some obser- 

 vations by Barnes and Hager* (1932) may be cited. A culture of 

 pneumococci was divided into four parts and to each portion there 

 was added 0.2, 0.3, 0.4, and 0.5 per cent respectively of formalin. 

 After storage at room temperature overnight, the cultures were 

 centrifuged and the supernatant fluids tested for free and com- 

 bined formaldehyde. In each case only about 0.05 per cent of for- 



* Unpublished. 



