286 THE PRINCIPLES OF IMMUNOLOGY 



They employed broth cultures of bacillus typhosus two to three weeks 

 old, killed by heating to 63 C. for one hour and preserved with 0.5 

 per cent, phenol. The vaccine was treated for sterility, standardized 

 and employed in doses of 750 to 1000 million organisms. In the same 

 year Pfeifrer and Kolle reported the demonstration of specific anti- 

 bodies following the immunization of man against the organism. Since 

 that time vaccines have been prepared in a large variety of ways and 

 preventative vaccination is now upon a highly satisfactory basis. Vac- 

 cination has been employed in military and civil life and has resulted 

 in a marked decrease in morbidity and mortality. The results obtained 

 in all civilized countries constitutes one of the greatest achievements 

 resulting from the study of immunology. 



Preparation of Vaccines. The organisms may be grown in broth or 

 upon agar. The broth culture or a salt solution suspension of an agar 

 culture may be killed or attenuated. The application of heat or chemi- 

 cals for the purpose of killing the organisms reduces in a certain 

 measure their antigenic value. If they are dried before being heated, 

 temperatures of 120 to 150 C. reduce the antigenic property very 

 little. Gay, however, points out that the measure of the antigenic value 

 depends upon the determination of different antibodies such as agglu- 

 tinins and bacteriolysins, but he notes that this offers "an indication 

 rather of the reaction of the animal body than a sure means of deter- 

 mining the degree of protection that has actually been afforded." 

 Numerous investigators have suggested the use of living bacteria, but 

 the knowledge that typhoid fever may exist as a septicemia without 

 intestinal lesions offers an objection, to the introduction of living or- 

 ganisms. It has been found extremely difficult to attenuate without 

 killing the bacteria, but it has been recommended that low degrees of 

 temperature, for example 53 C. (Leishman), the use of ether, alcohol, 

 various sugars and other chemical and physical agents may kill the 

 organisms without markedly reducing the antigenic properties. Certain 

 investigators have also suggested the employment of bacterial extracts, 

 but this method has not been widely employed. Gay and his collab- 

 orators (page 301) have claimed success in the therapeusis of typhoid 

 fever by the use of sensitized vaccines and have found that active 

 immunization progresses very satisfactorily, according to measurements 

 of specific antibodies, yet this method, if employed for vaccination, 

 is expensive and probably does not give sufficiently superior results to 

 justify its employment in large numbers of individuals. 



It is now recognized that the typhoid bacillus may be divided into 

 a number of strains on the basis of cultural and immunological prop- 

 erties. In certain countries, including the United States, a single strain 

 of the organism has been employed for vaccination, but in others a poly- 

 valent vaccine has been employed, the French using ten strains, The 

 organisms are grown on large agar surfaces, emulsified in salt solution 

 and killed by heat. They are then standardized and a preservative, 

 such as phenol, lysol or f onnaldehyde, added. Twenty-four hours sub- 



