568 BIOLOGY OF PNEUMOCOCCUS 



of culture. Serum and culture were injected intraperitoneally, 

 either simultaneously or one immediately following the other. A se- 

 rum was considered sufficiently potent if 0.2 cubic centimeter pro- 

 tected mice weighing from fifteen to twenty grams against 0.1 

 cubic centimeter of an eighteen to twenty-four-hour broth culture 

 of such virulence that 10" 6 cubic centimeter killed control mice of 

 similar weight. Survival of mice for ninety-six hours indicated pro- 

 tection. There were irregularities in the results obtained by this 

 method, but it served as a valuable means of controlling the po- 

 tency of serums by establishing minimum standards. Wadsworth, 

 Kirkbride, and Gilbert (1919) 1472 described the New York State 

 standard method of testing antipneumococcic serum which, in its 

 essentials, corresponded to that of the federal laboratory. In 1919, 

 the United States Public Health Service 1439 published the details 

 of the mouse protection test as used at the Hygienic Laboratory.* 

 Felton (1924) 396 experimented with varying amounts of Type I 

 culture in protection tests in an effort to overcome the irregular 

 results obtained by the governmental method. He defined a unit of 

 antibody as that amount which would protect mice against 0.5 

 cubic centimeter of a 1 to 10 dilution of an eighteen-hour broth 

 culture of such virulence that 10" 7 cubic centimeter killed mice in 

 thirty-six to forty-eight hours. This dose was calculated to con- 

 tain one million minimal lethal doses. In estimating the protective 

 power of an antibody solution, Felton tested varying dilutions of 

 the serum against a constant inoculum of culture in duplicate se- 

 ries of mice, as practiced by Neufeld (1922). 9TT Formerly the test 

 depended upon titrating a constant amount of serum against vary- 

 ing amounts of culture; here the reverse was true, that is, a con- 

 stant dose of culture was used against varying amounts of serum. 

 In 1928, Felton 402 presented the details of the protection test 

 developed in his investigations. The method was an improvement 

 over those previously used, but it was subject to limitations, recog- 

 nized by Felton, which will be considered later. 



* See Appendix. 



