PROPHYLACTIC TYPHOID INOCULATION. 31 



fore subplanted on agar tubes and incubated for a day or two. If a growth 

 appears, the emulsion is to be reheated; if not it can be considered sterile. 



The mode of immunization is the same as has been described for the 

 living bacteria. In general the dosage to be used may be larger. 



Small doses are injected at first, followed later on by increasing quanti- 

 ties at intervals of five to eight days. e.g. 



Intravenous inoculation of a rabbit with dead typhoid bacilli. 



Result. Protection against living virulent bacteria, appearance of 

 agglutinins, bacteriolysins, bacteriotropins and complement binding sub- 

 stances in the serum. 



i. /I. 1909. Rabbit No. I. i loopful of a typhoid agar slant culture killed at 60 and 



injected intravenously. 



6./I. 4 loopfuls of typhoid culture killed at 60 and injected intra- 



venously. 



12. /I. i culture of typhoid killed at 60 and injected intravenously. 



20. /I. Infection with i culture of the living typhoid bacilli injected 



intravenously. Animal remains alive. 

 Rabbit No. 2. Control. 



20. /I. Infection: 1/4 loopful of living typhoid bacteria intravenously. 



22. /I. f (death). 



The use of killed typhoid bacteria for prophylactic immunization has 

 recently been widely adopted. This has been stimulated to a great degree 

 by the successful experiments of Wright, and PfeifTer and Kolle. 



Wright's Method of Prophylactic Typhoid Inoculation. 



The vaccine or'ginally employed by Wright for these inoculations con- 

 sisted of highly virulent cultures of Bacillus Tpyhosus grown in broth for 

 twenty-four to forty-eight hours (sometimes even for four weeks), and 

 sterilized by heating at 60 C. The vaccine was then standardized, i.e., 

 the strength of the vaccine was fixed in accordance with another of known 

 strength, the dosage of which had been gauged by inoculations in man. 



The early form of standardization consisted in determining the toxicity 

 of the virus. Guinea-pigs weigh.'ng 250 to 300 gm. were inoculated sub- 

 cutaneously with 0.5, 0.75, i.o and 1.5 c.c. of the vaccine respectively. 

 Death to some of the animals would come in twelve hours to three days. 

 The amount required to kill a guinea-pig weighing 100 grammes or rather 

 the proportional fraction of the dose which proved fatal to the one of 250 to 

 300 gm. was taken as the standard dose for injection in man. Wright sub- 

 sequently found that better results were obtained, if the vaccine was pre- 

 pared from twenty-four hour cultures grown upon the surface of agar, and 

 after emulsification, standardized so as to contain 1,000 millions of typhoid 

 bacilli in every cubic centimeter. This method of standardization, the 

 details of which will be given in the chapter on Opsonins, is effected by 



