IMMUNOLOGICAL BEHAVIOR IO3 



The quantitative measurement of the reacting factors ^vas car- 

 ried out by Method III (Chapter 1) . 



All the stock strains tested, as well as their variants, were ca- 

 pable of producing highly potent toxic substances. The minimal 

 dose of reacting factors produced reactions only in a small per- 

 centage of rabbits in the majority of instances. Various multiples 

 of the minimal doses were tested in groups of ten rabbits. Six and 

 10 iniits, however, gave a high percentage of reactions (i.e., "jry 

 100 per cent) . 



Diagrams 1 and 2 represent the results of neutralization experi- 

 ments with various amounts of reacting factors of different toxic 

 filtrates mixed with constant amounts of certain imnnuie sera 

 carried out according to the method pre\iously described 

 (Shwartzman. 19.^0/;) {pp. 95, 97) . 



As is seen from Diagrams 1 and 2, two types of neutralization 

 were obtained, i.e., consistent and irregtdar neutralizations. The 

 irregular neutralizations which take place Avhen the amount of 

 reacting factors is increased beyond a certain maximum are most 

 likely due t(j the fact that the mixtiuxs contain a small amount 

 of free reacting factors so that only the rabbits possessing a high 

 degree of reactivity are able to respond with reactions. It does 

 not appear safe to make quantitative estimations of the neutraliza- 

 ])ility of a filtrate by determining the largest amount of react- 

 ing factors inei!;ula}ly neturalized by a serum since the exact 

 mechanism of irregular neutralization is not known as yet. This 

 type of neutralization offers only a rough cpiantitative comparison 

 of the degree of neutralizability of \'arious hltrates by a given 

 serum. Fairly accurate quantitative comparisons of the degree of 

 neutralizability of reacting factors derived from various filtrates 

 can be made, however, by determining the largest amoinit of 

 reacting factors consistently neutralized by a given serum. The 

 folloAving becomes evident from the analysis of data obtained. 



Various stock strains of B. iyjjhosus show striking differences in 

 the serum neutralizability of their reacting factors. Out of 4 

 strains chosen for this ^vork, 2 occupied extreme positions, one 

 shoAving a high degree of neiuralizability Avith strain homologous 

 and strain heterologous sera (Ty Tl stock and Sera S5 and Sc) 

 and another strain (Ty 159 stock) shoAving no consistent but 

 only irregular neutralizations w^ith the same sera. A horse serum 

 (Horses Bleedingiu) which was prepared by injection of mix- 

 tiUTS of various strains including Ty 159 stock also failed to give 



