PRODUCTION OF ANTIPNEUMOCOCCIC SERUM 595 



also found that long-continued immunization of the stock animals 

 resulted in the acquisition by the serum of non-specific immuno- 

 logical properties. The latter point has been considered in the de- 

 velopment of the so-called "rapid method" of producing rabbit 

 typing serums, in which the animals are subjected to an intensive 

 course of immunization and, when the titer of the serum is satisfac- 

 tory, the animals are exsanguinated. Experience at the Massachu- 

 setts laboratory has shown that, with properly selected cultures 

 killed by heating at 100°, rabbits may be immunized over a period 

 of at least a year and bled routinely every three weeks after a 

 course of twelve to fifteen injections. The amount of serum ob- 

 tained when the plan is followed reduces the cost of production 

 and, when the specificity of closely related strains is carefully con- 

 trolled, as suggested in the paper by Barnes and Wight, 88 cross- 

 reactions with the serum are avoided. The methods recommended 

 by the authors are described in the Appendix, page 663. 



Rabbit serum intended for use in the Neufeld method should be 

 tested for both potency and type-specificity. Cooper and Walter 

 (1935) 275 recommended a minimal agglutinative titer of at least 

 1 to 200, with freedom from cross-reactions, and that each serum 

 be tested for its ability to cause a characteristic capsule swelling 

 of pneumococci of the homologous type. 



Some workers have maintained that rabbit serum for use in the 

 Neufeld test must be used in undiluted state. The claim is not nec- 

 essarily valid, however, for in the authors' experience completely 

 satisfactory results are obtainable, at least with certain pneumo- 

 coccal types, if highly potent serums are diluted as much as 1 to 5 

 to 1 to 10 with normal rabbit serum. 



As in the case of therapeutic serums, it is recommended that 

 standard methods of producing diagnostic serum for the type de- 

 termination of all known pneumococcal types should be universally 

 adopted and put into effect. A movement to bring about the fulfil- 

 ment of the object has been initiated in the United States. 



