IMMUNOLOGICAL BEHAVIOR gg 



the serum. In the example cited, 1:2000 ^voiild be considered the 

 titer. 



Normal sera from horses, goats and rabliits uitli some excep- 

 tions, failed to neutralize the skin-preparatory factors in a large 

 percentage of rabbits. These exceptional sera neutralized the skin- 

 preparatory factors only in low dilutions (1:20, 1:2). A large 

 group of heterologous immiuie sera containing homologous ag- 

 glutinins of high titer were also tised for neutralization experi- 

 ments. Scarlet fever, erysipelas, B. coli, B. dysoiteriae Shiga, 

 Flexner and Mt. desert, and B. avicida sera produced no neutral- 

 ization of the B. typhosus skin-preparatory factors in spite of the 

 fact that some of the sera contained agglutinins against B. ty- 

 phosus. The closely related sera, paratyphoid A and B, were able 

 to netitralize the B. typhosus skin-preparatory factors in various 

 proportions and, as woidd be expected, agglutinated B. typlwsus 

 in a fairly high titer. The rabbits employed in these experiments 

 could also be divided into three groups, namely, those sho^ving 

 neutralization in highest dilutions (HN) , those showing neutral- 

 ization only in lower dilutions (LN) and those showing no neu- 

 tralization (NN) . 



As may be seen from the above description, there are inherent 

 difficulties in the method, ho^vever, which can be avoided only 

 pr()\ided large grotips of animals are used. The difficulties are 

 the possible spreading of the neutralizing antibodies to the con- 

 trol sites; the high death rate of animals from the intravenous 

 injection of large doses of reacting factors, necessary for elicita- 

 tion of consistent reactions in a number of sites prepared; and 

 the xariability in the response of animals to completely neu- 

 tralized mixttnes. After controlling these variotis factors by the 

 use of large groups of animals there ^vas afforded, ho^vever, im- 

 questionable proof that the skin-preparatory factors of the phe- 

 nomenon can be specifically neutralized by immune sera. 



EFFECT OF NORMAL AND IMMUNE SERA UPON REACTING FACTORS 



A large series of experiments was carried out in order to deter- 

 mine ^vhether the reacting factors can be specifically neutralized 

 by immune sera. In the basic experiments the antityphoid sera 

 were obtained from horses and rabbits. 



The immunization of horses was carried out by simultaneous Aveekly sub- 

 cutaneous and intravenous injections. Filtrates of six day old B. typhosus 

 cultures in tryptic digest broth, as well as toxic substances precipitated by 



