528 APPLICATION OF METHODS OF BACTERIOLOGY 



Major Russell has also shown by a very careful study that 

 children under five years of age may be safely vaccinated 

 if appropriate doses of the vaccine be employed. 



The Vaccine. The agent used in vaccination is typhoid 

 bacilli that have been killed by heat. In some instances 

 living, sensitized typhoid bacilli have been employed with 

 good results, but as the bulk of experience has been obtained 

 with the dead cultures and as this is much the more simple 

 procedure it is probable that it is the method that will be 

 generally adopted. 



The vaccine is prepared as follows: A proven culture of 

 bacillus typhosus is grown on nutrient agar-agar at body 

 temperature for eighteen to twenty hours. The growth is 

 then carefully washed from the surface with a small quantity 

 of sterile physiological salt solution. This emulsion is then 

 heated in a water bath to 53 C. for one hour, after which 

 it is diluted with sterile salt solution to a point at which a 

 billion bacilli are contained in a cubic centimeter of the 

 emulsion. Finally tricresol in the proportion of 0.25 per 

 cent, is added as a preservative. Before using such 

 vaccine its safety: i. e., its freedom from objectionable 

 qualities, especially from the germs of tetanus, is invariably 

 tested, as is also its efficiency in calling forth the customary 

 reactions of intoxication and resistance. These tests are made 

 upon such sensitive reagents as mice, guinea-pigs, and rabbits. 



The original vaccination consisted in the subcutaneous 

 injection of a volume of emulsion equivalent to 500 million 

 bacilli followed on the tenth and twentieth days with doses 

 equivalent to 1000 million bacilli; that is to say, the first 

 dose is 0.5 c.c. of the above-mentioned emulsion, while 

 the second and third doses are 1 c.c. each. 



