586 BIOLOGY OF PNEUMOCOCCUS 



preparations tested and their therapeutic efficacy. Moreover, the 

 method should be equally applicable to unconcentrated and con- 

 centrated products. From the theoretical standpoint, at least, 

 some method utilizing the principle of optimal proportions ap- 

 pears to meet these requirements. As long as the mouse protection 

 test remains the accepted procedure for assaying antipneumococ- 

 cic serum, a stable, standard serum should be available for general 

 use, only standard cultures maintained under uniform conditions 

 should be employed in the test, and a technique should be adopted 

 that would be acceptable to all engaged in the manufacture and use 

 of the products. 



Confusion has existed because of a lack of any satisfactory 

 definition of a unit of antibody. The unit as defined by Felton 

 (1924) 896 furnished a convenient working basis, but experience has 

 shown that the number of lethal doses of pneumococci against 

 which a given serum will protect is too variable a factor to serve as 

 a criterion for establishing the unit. A stable, desiccated standard 

 serum of which a given weight contains, by international agree- 

 ment, one unit of antibody as suggested by Hartley and Smith, 696 

 would, for the time being, supply the need. In the event that a pre- 

 cipitin test is substituted for the mouse protection method of 

 standardization, it is possible that the standard of comparison, as 

 suggested by Felton and Stahl, should be a uniform and satisfac- 

 tory preparation of type-specific polysaccharide, rather than a 

 control serum. 



A comprehensive discussion of the standardization of antipneu- 

 mococcic serum and concentrates is to be found in the latest com- 

 munication of Felton and Stahl (1937). 433 The report comprises 

 the results of a restudy of the various methods advocated for de- 

 termining the potency of serum. The original report should be con- 

 sulted for the details of the several tests carried out in the study 

 but, because of the pertinency of the conclusions, some of them are 

 quoted here. 



