PROPHYLACTIC TYPHOID INOCULATION 33 



Wright's Method of Prophylactic Typhoid Inoculation. 



The vaccine originally employed by Wright for these inoculations con- 

 sisted of highly virulent cultures of Bacillus Typhosus 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 weighing 250 to 300 gms. were inoculated 

 subcutaneously with 0.5, 0.75, i.o and 1.5 c.cm. of the vaccine respec- 

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

 three days. The amount required to kill a guinea-pig weighing 100 gms. 

 or rather the proportional fraction of the dose which proved fatal to the 

 one of 250 to 300 gms. was taken as the standard dose for injection in 

 man. Wright subsequently found that better results were obtained, if the 

 vaccine was prepared from twenty-four hour cultures grown upon the sur- 

 face of agar. The growth is then washed off in physiological 

 Preparation, saline solution. This emulsion is sterilized by subjecting 

 it to a temperature of 55 to 60 C. for one hour, after which 

 the number of bacteria is computed by Wright's method (see Standard- 

 ization of Vaccines in chapter on Opsonins). After this the emulsion is 

 further diluted with physiological salt solution containing 0.5 per cent, 

 carbolic or 0.25 per cent, trikresol in such a manner that two or three 

 different concentrations are secured, one containing 500 million killed 

 typhoid bacilli per c.cm., one containing 1000 million per c.cm., and one 

 containing 2000 million per c.cm. 



The particular strain of typhoid bacillus employed for the vaccine 

 varies. Some use a strain isolated by Leishman in 1900. This is selected 

 not on account of its degree of virulence but on account of its property 

 of being able to stimulate the formation of a great amount of antibodies. 

 The editor and others employ a mixture of eight or ten different strains 

 with perhaps one or two paratyphoid strains. 



The typhoid vaccine or typho-bacterin as it is frequently called is 

 administered subcutaneously, usually in the arm at the insertion of the 

 deltoid muscle. The needk should not enter the muscle or find its way 

 between the layers of the skin. The arm should be cleansed as for any 

 other injection with alcohol and iodine. 



The dosage almost uniformly employed consists of 500 million 

 Dosage, bacteria for the first injection and 1000 million for each of the 

 two subsequent injections at intervals of eight to ten days. 

 If, however, such an extended period of time is not available, then two in- 

 oculations will suffice, the first dose 1000 million and the second dose 



