ANTIDYSENTERIC SERUM 



237 



weeks at 37 C., in alkaline broth similar to that used for preparing diph- 

 theria toxin; this should be neutralized to phenolphthalein, and 7 c.c. 

 normal soda solution to a liter added. The minimal lethal dose of the 

 mixed unfiltered cultures is determined by giving young rabbits increas- 

 ing doses intravenously, in order to obtain a guide as to the proper dose 

 for immunization. Fatal doses produce severe diarrhea and paralysis 

 of the extremities, with rapid loss in weight. Rabbits and horses are 

 quite susceptible to the toxin; guinea-pigs and mice are more resistant. 



TABLE 3. METHOD OF DETERMINING THE MINIMAL LETHAL DOSE 

 OF DYSENTERY CULTURE 



In this instance the minimal lethal dose was 0.2 c.c. and subsequent 

 cultures of the same strains, grown under similar conditions, showed this 

 dose to remain quite constant. 



It is good practice to keep the cultures growing during the entire 

 time of immunization. Cultures may, however, be grown for three 

 weeks, filtered through porcelain, and with the addition of 0.5 per cent, 

 phenol, the toxin preserved for long periods of time. The minimal 

 lethal dose of such a toxin is determined in the manner directed above. 



Immunizing the Animals. Since horses are quite susceptible, the 

 initial dose of unfiltered and unheated culture should not be larger 

 than the minimal lethal dose for a young rabbit. The dosage is grad- 

 ually increased, and the injections are given siibcutaneously for from 

 four to six months, after which several injections of from 300 to 350 c.c. 

 may be given intravenously at one time. If at any time diarrhea and 

 other symptoms of toxemia are well marked, subsequent doses should 

 be smaller and should be given at longer intervals until a higher immu- 

 nity is produced. 



Instead of using bouillon cultures, young agar cultures may be used, 

 the bacilli being grown for seventy-two hours, and one-tenth of an ordi- 

 nary slant being given as the first dose. The early doses are heated to 

 60 C. for an hour and injected subcutaneously; the later doses consist 

 of cultures washed from 30 to 40 tubes, and are given intravenously. 



