426 PATHOGENIC MICROORGANISMS 



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 fifty per cent, and a reduction of the mortality of those 

 who became infected in spite of inoculations of fifty 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 

 differences which have been recently discovered and alluded to would 

 make it seem that no single strain can be expected to produce anti- 

 bodies which would protect against all other strains. It is not impos- 

 sible that some individual strain may combine the antigenic properties 

 of the entire group. This, however, has still to be worked out. 



The method of Peiffer 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. 



Recent extensive tests in the United States Army, observed by Rus- 

 sell, 1 seem to 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. ' Eighte.en-hour agar 

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

 mate concentration of one billion to the c.c. The suspension 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 and mouse inocu- 

 lated to insure sterility. For immunization 3 to 4 doses are given 

 ranging in quantity from 500 million to one billion at 7 to 10 day 

 intervals. The protection probably lasts about 2 years, though this is 

 not certain. 



Another point of importance in this connection has recently been 

 raised by Metchnikoff and Besredka. 2 They vaccinated chimpanzees 

 with typhoid bacilli and found that when emulsions of the clear bac- 



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



2 Metchnikoff and Besredka, Am. de Tinst. Past.., 1911. 



