rf'. 

 IMMUNITY TO LOCAL SKIN REACTIVITY 135 



became imnume to 150 B. typlwsus reacting factors. Here again, 

 the immunity was specific, since the rabbit remained sensitive to 

 meningococcus reacting factors. In addition, it was possible to 

 inmiunize it also to these factors within t^vo weeks. The rabbit, 

 thus imminiized to reacting factors of t^vo microorganisms, re- 

 mained, however, sensitive to a third microorganism; i.e., B. coli. 

 A third rabbit illustrated an active acquired immunity to graded 

 amoinits of B. typhosus reacting factors. The immunity was in- 

 complete since retests with 300 and 350 tniits elicited strong reac- 

 tions. On the other hand, a foiuth rabbit demonstrated total 

 failtue to acquire active immunity, and a fifth rabbit showed a 

 partial acqtiired immunity dining the course of immunization 

 to 30 reacting units, with subsequent susceptibility to larger doses 

 on a retest in a Aveek. 



It became evident, therefore, that in order to demonstrate the 

 existence of this immunity, a sufficiently large group of animals 

 and graded amounts of toxic material shoidd be employed. 



Group Ila. The rabbits of this group showed a spontaneous 

 partial immunity inasmuch as they presented reactions with one 

 reacting unit, but proved sensitive to 15 iniits of the same filtrate, 

 ^vhen retested one ^\eek later. A few weeks later, the sensitivity 

 Avas followed by a prompt acquired imminiity ^vhich ^vas of a non- 

 specific natine. The animals gave no reactions when reinjected 

 Avith larger amoiuits of the same filtrates as Avell as Avith large 

 doses of other filtrates {i.e., B. coli, B. typhosus, B. typhosus 

 rough and meningococcus of other serological groiq^s) . 



Group lib. These rabbits possessed a non-specific immunity as 

 concerns the phenomenon inider consideration, inasmuch as in 

 contrast to Group Ila none of the injections of large doses of 

 heterologous filtrates elicited reactions at any time. 



On the basis of the above observations it then becomes neces- 

 sary to differentiate between active specific and non-specific ac- 

 quired immtniity to the phenomenon of local skin reactivity to 

 bacterial filtrates. The active specific immunity can be induced 

 by immunization of highly susceptible rabbits with the toxic 

 material. The non-specific immunity is elicited in rabbits pri- 

 marily showing partial spontaneous immimity. The question of 

 active acquired immunity to the phenomenon under discussion 

 has also been studied by other investigators. 



According to Burnet (1931), repeated reactions coidd be 

 elicited in rabbits without diminishing their reactivity. In one 



