134 LOCAL ILSSLE REACrrLVLFY 



Active Acquired Immunity : 



In view of the a()()\e lindiiiti^s, it was of finther interest to 

 determine whetlier iintniniity could be also attively acquired. 

 Tn some experiments rabbits were imnumized by one or two 

 intradermal injections of bacterial filtrates. The intradermal 

 vaccination with B. lyjjhosits cidtiue filtrates induced active im- 

 miniity to the phenomenon of local skin reactivity to B. typhosus 

 and also conferred resistance to the lethal effect of the toxic sub- 

 stances. 



The existence of active acquired immimity having l)een demon- 

 strated, it Avas necessary to determine the specificity oi this im- 

 numity with graded amotuits of bacterial filtrates. In these experi- 

 ments rabbits were tested with one unit of B. typJiosus reacting 

 factors. According to their response to this injection, they could 

 be grouped as I — sensitive animals, i.e., giving reactions with one 

 reacting luiit; and II — refractory animals, i.e., sho^ving no reac- 

 tion ^vith one reacting unit. The latter group could be finther 

 sid)divided into Ila — those ^vhich had only partial immunity, 

 inasmuch as retest ^vith 15 reacting luiits one week later produced 

 reactions in them; and lib — those which did not sho^v any reac- 

 tions when later retested with larger doses of reacting units. 



The tests were then followed by repeated attempts to reproduce 

 the phenomenon in the tested animals with increasing amoiuits 

 of various bacterial filtrates with the folloAving results: 



Group I. Rabbits highly sensitive to the phenomenon, i.e., 

 those reacting to one intravenous iniit, acquired an active specific 

 immunity to it by means of combined intradermal and intra- 

 venous immimization with toxic bacterial filtrates. As might be 

 expected the animals of this group showed indi\ idual variations 

 in their response to the process of immunization. Some of them 

 failed to acquire a state of immimity, ^vhile others showed various 

 grades of it. 



Thus, one rabbit was sensitive to one B. typliosus reacting 

 unit. Two weeks after the first injection there was obtained a 

 doubtful immunity to 30 units and three and four weeks later 

 the rabbit sho\ved complete immunity to as many as 60 and 100 

 iniits. The immimity established ^vas specific, inasmuch as retests 

 ^vith meningococcus filtrate elicited severe reactions. Another rab- 

 bit at first sensiti\'e to one reacting luiit of B. typliosus, promptly 



