546 BIOLOGY OF PNEUMOCOCCUS 



Subsequent to the division of pneumococci into types by Dochez 

 and Gillespie, 322 Cooper, Edwards, and Rosenstein, 272 in separat- 

 ing Group IV pneumococci into twenty-nine types, found little 

 cross-protection of monovalent serums against heterologous 

 strains. For example, a concentrated Type II serum contained 

 only ten to twenty units against a Type V culture. In 1932, how- 

 ever, Cooper, Rosenstein, Walter, and Peizer 274 suggested that, be- 

 cause of the marked cross-reactions of many Type V strains with 

 Type II antiserums and vice versa, it might be advisable to pre- 

 pare an antiserum potent for both types. Observations by Barnes 

 and Wight (1936) 88 which suggested that, under stated condi- 

 tions, Type V Pneumococcus might become transformed into Type 

 II Pneumococcus, led them to make a recommendation in accord 

 with that of Cooper and her colleagues. 



Aside from such a basis for the manufacture of bivalent or poly- 

 valent serums, there are other factors which should be taken into 

 consideration. In some laboratories, serum bivalent for Types I 

 and II has been produced. Since there has been no demonstration 

 of close relationship between the types, the only justification for 

 the custom appears to be one of economy. This explanation also 

 holds true in the case of serums polyvalent for other pneumococcal 

 types. Horses appear to tolerate injections of a vaccine contain- 

 ing pneumococci of several types as well as of an antigen made 

 from a single strain. Antibodies active against the various strains 

 used can thus be produced in one animal instead of using separate 

 horses for each type serum desired. Whether the economy is real or 

 apparent is a question which remains for the producer to deter- 

 mine. On the other hand, an impression, confirmed, at least in part, 

 by Cooper and her associates, 272 has been gained, that higher pro- 

 tective powers are developed in monovalent immunization than is 

 the case when strains of several types are injected into producing 

 animals. Definite evidence to support the hypothesis is, however, 

 lacking. With the rapid and accurate Neufeld method of typing 



