682 PATHOGENIC MICROORGANISMS 



carbolic acid. Later, Wright ll8 employed bacilli grown in a neutral 

 1-per-cent pepton bouillon in shallow layers of flasks. 



Great importance is attached both to the virulence of the typhoid 

 strain, which may to a moderate extent be standardized by passage 

 through guinea-pigs, and to care in using low temperatures for final 

 sterilization. The temperature recommended by Harrison, is 52 C. 

 after which the cultures are carbolized. 



It is nevertheless extremely difficult to tabulate satisfactory statis- 

 tics from a mass of experiments observed by a large number of indi- 

 viduals. On the whole, however, it seems fair to state that advan- 

 tageous results followed the active immunization practiced by Wright. 

 Wright's own estimation, in a careful attempt to present the subject 

 fairly, gives a reduction of the morbidity from typhoid fever in the 

 British army of 50 per cent, and a reduction of the mortality of those 

 who became infected in spite of inoculations of 50 per cent also. It is 

 not at all impossible that a number of different strains will have to be 

 used eventually for the ideal vaccine, inasmuch as the antigenic differ- 

 ences which have been recently discovered would make it seem that no 

 single strain can be expected to produce antibodies which would protect 

 against all other strains. It is not impossible that some individual 

 strain may combine the antigenic properties of the entire group. This, 

 however, has still to be worked out. 



The method of Pfeiffer and Kolle consists in the injection of salt- 

 solution emulsions of fresh agar cultures sterilized at 60 C. The 

 results reported were in general favorable. 



Extensive tests in the United States Army, observed by Russell, 119 

 have removed any doubt which may have existed as to the efficacy of 

 prophylactic typhoid vaccination. Russell's statistics show a steady 

 decline of typhoid in the U. S. Army beginning with the introduction 

 of compulsory vaccination in 1910. In 1913 there was but one case 

 among over 80,000 men. 



The method at present employed is as follows: The "Rawlings" 

 strain of typhoid, obtained from Wright, is used. Eighteen-hour agar 

 cultures in Kolle flasks are washed off with sterile saline to an approxi- 

 mate concentration of one billion to the cubic centimeter. The sus- 

 pension is killed at 53 C. for one hour and 0.25 per cent tricresol is 

 added. Aerobic and anaerobic culture controls are made and a rabbit 



118 Wright, Brit. Med. Jour., 1901; Lancet, Sept., 1902; Brit. Med. Jour., Oct., 

 1903. 



119 Russell, Am. Jour, of Med. Sc., cxlvi, 1913. 



