Antityphoid Vaccination

Abstract

read before the United Services Medical Society and printed in extenso in the Journal of the Royal Army Medical Corps. Although medical practitioners do not actually need a detailed acquaintance with bacteriological methods, nevertheless it enables them to follow the rationale of vaccine treatment when they have a clear idea of the process by which a vaccine is prepared. The following is a summary of the various steps of the technique required in making an anti-typhoid vaccine, which consists of a sterilised broth culture of the typhoid bacillus. The broth is ordinary nutrient broth brought to a reaction of +10 (Eyre's scale)?that is to say, it is made alkaline to a certain definite degree. It is sterilised in the autoclave for a minimum period of three-quarters of an hour at 120? C. After cooling over night, it is incubated for 48 hours at 37? C., and then kept for two or three days at room temperature in the dark to prove its sterility.The broth is not sterilised in bulk, but in flasks containing not more than 300 c.c.The purity of the culture is verified by plating, by titration with an anti-typhoid serum, by direct microscopical examination, and by cultural tests.The flasks are then inoculated and incubated for 48 hours at 37? C., and are placed in a horizontal position in the inciibator.A dense growth of typhoid bacilli is obtained with the flasks in this position, owing to the fact that the typhoid bacillus grows more readily in the presence of an abundant supply of oxygen. All the apparatus, with the exception of the bottles, is sterilised in the autoclave for three-quarters of an hour at 120? C. The bottles are sterilised by dry heat.The contents^ of a series of flasks are then mixed and measured in a graduated jar; a batch of culture as a rule consists of about 4 litres before it is diluted. Measured volumes of culture are then run off into suitable flasks by means of " two-way tubes."These tubes are then removed, and samples of the growth taken and tested for purity. This precaution is necessary in the preparation of all vaccines, but more especially so when a large quantity is prepared from many flasks. The flasks are closed with their original plugs, which are then covered with waxed paper. This is perforated in order that an even pressure may be maintained, thus ensuring that the temperature of the culture will correspond with the control flask in the bath. The flasks are then placed in a water-bath at a temperature of 45? C. A thermometer placed in the control flask will enable one to ascertain the exact temperature of the culture.The bath is kept at a temperature of 45? G. for half an hour to allow the temperature of the culture to rise to that of the bath. The temperature of the whole is then gradually raised until the thermometer inside the control flask stands at 53? C.After an hour and ten minutes at 53? C., during which time the flasks 'are repeatedly shaken, they are taken out of the bath and cooled down. The reason for this cooling is that it has been found by experiment that the potency of ...