9.,[)S LOCAL ILSSUE REACTIVITY 



and ()\ei ()() units ol C.rouj) III ic.utiuL; lac tors, i.e., a potency 

 wliicli may he considered cjiiitc hi^li and didu nil to obtain even 

 following a coinse of j^rolonj^cd innnuni/ation. After tiie fourth 

 injection the titer dropped and remained at a low level for several 

 months in spite of persistent immunization. The agglutination 

 and precipitation titers of sera of trial l)lcedings remained at 

 approximately the same levels coincidentally with wide fluctua- 

 tions in concentration of neutralizing antibodies in tiiese horses. 



The observations thus far made suggest that anti-meningococcus 

 neutralizing sera may be obtained in an economical way. The 

 horses should receive ueekly subcutaneous injections of active fil- 

 trates and also intravenous injections of heat-killed \'accines. They 

 stand the treatment (juite well because small doses of the mate- 

 rials may bring al)out the desired results. The process of alternat- 

 ing immimization periods ^vith periods of rest enables one to 

 employ the same horses for a considerable length of time. It is 

 important, hoAvever, to test frequent bleedings from the very 

 beginning of immunization. It appears that the optimimi time for 

 trial bleedings is six days after each injection. Inasmuch as it \vas 

 observed that eight days after the injection, a previously high 

 concentration of antibodies may come do^vn, large bleedings 

 should be done as (piickly as possiljle after the trial bleedings 

 (provided, of course, the latter sho^v a high titer) . This is easily 

 carried out as follows: 



The necessary groups of rabbits are prepared ])y intradermal in- 

 jections of the active filtrate on the morning of the day before 

 the trial bleeding. The rabbits receixe intravenous injections of 

 the mixtures to be titrated on the morning of the trial bleedings. 

 The residts are read early in the afternoon, i.e., about six to 

 eight hours after the trial bleeding. It is of interest that a nmnber 

 of previous authors xvho attempted to obtain antibodies protective 

 against lethal effect of meningococcus toxic substances, i.e., endo- 

 toxins and live cultures, made observations comparable to those 

 reported here. 



Gordon concluded horn his experiments on the production of 

 anti-endotoxin in rabbits that it is essential to avoid overdosage 

 (1920). Grilhth (1920-21) using Amoss and Wollstein's method 

 found that excessive or insufficient doses (particularly the third 

 of their series) brought about a fall in the j^rotective potency of 

 sera. Murray (personal communication) , who attempted to titrate 

 the protective power of sera, met Avith a number of disconcerting 



