426 PATHOGENIC MICROORGANISMS 



the quantity of bacilli fatal for 100 grams of guinea-pig. The dose may 

 also, according to Wright, be regulated by making numerical counts of 

 the emulsions used, by his usual method of counting against red blood 

 corpuscles, and using for the first injection 750 to 1,000 millions of dead 

 bacteria. The second injection, given after eleven days, should be double 

 this quantity. Usually the first dose is followed by local inflammatory 

 symptoms and the general systemic symptoms of toxemia. These, 

 however, usually disappear after forty-eight hours. 



Although the observations of Wright are extensive, it is nevertheless 

 extremely difficult to tabulate satisfactory statistics 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 

 distinctly advantageous results followed the active immunization prac- 

 ticed 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. Combining these two results, the actual reduction 

 of the death rate by the method of vaccination would appear to 

 amount to at least seventy-five per cent. 



The method of Pfeifler and KoUe, originally used by them in their 

 experiments, has been extensively carried out by German observers 

 upon the army taking part in the late East African campaign. 



Roughly, the method consists in the injection of salt-solution emul- 

 sions of fresh agar cultures sterilized at 60° C. The results reported 

 from a large material were in general favorable, indicating that the 

 morbidity of all the troops taking part was reduced by the inoculation 

 and that the death rate among the inoculated persons was lower than 

 that among normal individuals. 



Recent extensive tests in the United States Army, carefully observed 

 by Russell^ and others, seem to have removed any doubt which may have 

 existed as to the efficacy of prophylactic typhoid vaccination. How- 

 ever, another point of importance in this connection has recently been 

 raised by Metchnikoff and Besredka^. 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- 



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



2 Metchnikoff and Besredka, Am. de I'Inst. Past., 1911. 



