ANTI-TYPHOID VACCINE 367 



The disease has also been treated with a vaccine (con- 

 sisting of a killed culture) with promising results by Semple, 

 Smallman, Leishman, and others. The initial dose is 

 40-100 millions, and. the amount is cautiously increased 

 up to 300-400 millions. 



Anti-typhoid vaccine. Wright first prepared an anti- 

 typhoid vaccine by the following method. 1 A typhoid 

 culture of moderate virulence (the virulence being kept 

 up by intraperitoneal passage through guinea-pigs) is 

 grown in peptone beef broth in flasks at 37 C. for from 

 fourteen to twenty-one days. The flasks are then so 

 heated that their contents attain, and remain at for a 

 few minutes, a temperature of 60 C. To obtain uniform 

 toxicity, the contents of several flasks should be mixed, 

 and to safeguard the vaccine from contamination one 

 twentieth of its volume of 10 per cent, lysol is added. 

 Various ingenious devices have been adopted by Wright 

 and Leishman to prevent contamination and for stan- 

 dardisation. 



The immunising power of a typhoid vaccine depends 

 upon the number of bacilli it contains, and on the particular 

 strain of bacillus used. The vaccine is standardised by 

 counting the number of bacilli it contains by Wright's 

 method (p. 220). Leishman 2 now cultivates for about 

 forty-two hours, and the bacteria are killed by heating to 

 53 C. for one hour, the higher temperature having proved 

 to be deleterious, and after cooling 0*25 per cent, of lysol 

 is added ; it is not necessary to employ a virulent bacillus. 

 In the early days the symptoms produced by the inocula- 

 tion were often severe, but with more moderate methods 

 are now hardly appreciable. Two doses of the vaccine 

 should be given, with an interval of about ten days between 

 the two, the doses being 500 and 1000 millions respectively. 



1 Wright and Semple, Brit. Med. Journ., 1897, vol. i, p. 256. 



.2 gee Journ. Roy. Inst. Pub. Health, vol. xviii, 1910, pp. 385, 440, 513. 



