IMMUNITY TO LOCAL SKIN REACTIVITY 143 



B. t\j)hosus antibodies are encountered in normal and heterol- 

 ogous imminie horse sera, the sera "were also tested for agglutinins, 

 precipitins and neutralizing antibodies. Anti-meningococcus and 

 normal horse sera in a dose of 4 c.c. per kilo of body weight, 

 failed to protect against 40 reacting iniits, while the same dose 

 of anti-typhoid horse serinn protected against 180 reacting imits. 

 The normal and heterologous sera employed contained anti-ty- 

 phoid antibodies, the concentration of ^vhich, however, in 4 c.c. 

 {i.e., 320 and 240 units, respectively) was insufficient to neu- 

 tralize i)i vivo 40 reacting iniits, since, as described above, it is 

 necessary to have for this volume of serimi eleven times more 

 antibodies for in vivo than for in vitro neutralization. In an- 

 other grotip 7 c.c. of anti-meningococcus horse serum protected 

 against 40 B. typhosus reacting iniits. It is obvious that this \)\o- 

 tection could be easily attributed to the presence of anti-typhoid 

 normal antibodies, since in 7 c.c. there were present 420 neu- 

 tralizing units, or more than ten times the amount required for 

 in vitro neutralization. From these results it can be safely con- 

 cluded that passive immunity to B. typhosus reacting factors is 

 specific and depends on the concentration of homologous, normal 

 and immune neutralizing antibodies. 



It is also note^vorthy that there may occur a "prozone" effect 

 of large amoinits of serimi. The "prozone" effect in neutralization 

 experiments i)i vitro ^vas also frequently observed. 



Some studies ^vere also made on the dination of passi\e im- 

 miniity to B. typhosus reacting factors. It appeared that the 

 immimity established itself immediately after the intraxenous 

 injection of immune serum, and that one-half hoin- after the 

 serum injection the protection ^vas more effective. No definite 

 conclusi(jns coidd be draxvn, however, since the "prozone" effect 

 of seriun, just pointed out, coidd serve as a soinxe of error. In- 

 deed, it is possible that dining the half hour interval, a part of 

 the antibody \vas eliminated and thus the "prozone" effect ^vas 

 avoided. 



Two exjjeriments were carried out in ^vhich the intcrxal oi 

 time allowed between serum and filtrate intravenous injections 

 was one and one-half and two and one-half hours, respectively. 

 Each of the rabbits received 3000 neutralizing units and 100 react- 

 ing units. The protection was complete in both groups. Longer 

 intervals of time were not studied. 



It was of considerable interest to determine whether the oc- 



