420 PATHOGENIC MICROORGANISMS 



It is nevertheless extremely difficult to tabulate satisfactory statis- 

 tics from a mass of experiments which must of necessity be observed by 

 a large number of individuals, in all of whom the personal equation 

 modifies the results of the observations. On the whole, however, it seems 

 fair to state that advantageous 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 ty- 

 phoid 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. 



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 from a large material 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 "Rowlings" 

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

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

 imate 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 inter- 

 vals. 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- 

 teria were used, protection was only slight. Better results were ob- 

 tained that is, apparently complete protection within 8 to 10 days, 

 when living sensitized bacteria were injected. (Bacteria which had 

 been exposed to the action of inactivated immune serum.) Broughton 3 



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



2 Metchnikoff and Besredka, Am. de 1'inst. Past., 1911. 



3 Brought, C. R. de 1'Acad. des Sc., cliv, 1911. 



