REACTIVITY TO VARIOUS MICROORGANISMS 33 



In tlie Foregoing maiinci, highly potent prep:nations were ob- 

 tained Irom meningococcus ot xarioiis serological groups. Several 

 straiirs ol each group Avere tested. All the materials pre}:)ared since 

 i();o were titrated, as a routine, lor reacting potency against a 

 constant skin-preparatory dose (Method III) . In this test a single 

 site was prepared ordinarily by an injection ot 0.25 c.c. ot filtrate 

 diluted 1:2. The tollowing is the range of the reacting potency 

 of numerous preparations derived from \arious serological groups 

 of meningococcus: 



Group 1, strains 44D and 44F — 500 to 1500 reacting units; 

 Group 1, strains 397, 130, and 401 — 400 to 700 reacting units; 

 Group 2, strain 383 — 400 to 1350 reacting units; Group 3, strain 

 44B — 600 to 4000 reacting units; Group 3, strains 39() and 101 — ■ 

 500 to 1000 reacting tuiits. 



No extensive titrations were carried out on the skin-prepara- 

 tory potency of meningococcus "agar ^vashings" filtrate. The im- 

 pression \vas, howexer, gained that dilutions not higher than 1:25 

 should be employed for rabbits receiving 25 reacting tmits intra- 

 venously in order to obtain not less than 75 per cent of positive 

 results. 



Most of the work in the past years xvas carried out with the 

 strain 44B and on frequent occasions, titers as high as up to 4000 

 were obtained. From the analysis of the residts just recorded, it 

 may be safely stated that Group 3 strains yield toxic materials of 

 the highest potencies xvhilst strains of Groups 1, 2, and 4 fluctuate 

 within the limits of a lower range. As will be discussed again later, 

 the selection of the strain is a highly important consideration if 

 one wishes to obtain potent materials. In addition to the above 

 enumerated strains a number of cultures recently isolated from 

 sj)inal fluid of meningococcus meningitis cases xvere tested for 

 their ability to produce the active principles. In all, about 15 

 various strains were employed. No serological identification xvas 

 done. The average titers obtained ranged between 200 and 2400 

 reacting luiits, per 1 c.c. of "agar xvashings" filtrate. 



Pabst and Branham (1933) also found that with some "agar 

 washings" filtrates of meningococcus pronoiniced hemorrhagic 

 necrosis xvas obtained in dilutions as high as 1:800 xvhilst xvith 

 others the activity was much less. In their experiments there 

 seemed to be no relation between the activity of the filtrates and 

 serological grotiping though some indi\'idual strains regularly 

 produced more active filtrates than others. Length of time during 



