180 BACTERIOLOGY. 



they distributed more or less generally throughout the 

 body (bacterisemia) ? 



Note whether the virulence of the organism is main- 

 tained when grown for several generations on artificial 

 media, or whether it soon becomes attenuated. Which 

 culture-medium is best suited to conserve the virulence 

 of the organism ? In what manner does its environ- 

 ment influence the virulence ? If the virulence is readily 

 lost, may it be regained by any of the known methods ? 



Ascertain whether the organism forms a soluble toxin 

 when grown in fluid media, as sugar-free bouillon. If 

 toxin is formed, ascertain whether the antitoxic state is 

 readily induced in susceptible animals. 



If no soluble toxin is formed, ascertain whether ani- 

 mals may be immunized by the injection of sub-lethal 

 doses of dead or living cultures. Is a bactericidal immu- 

 nity induced by this means? Does the serum of immune 

 animals possess protective and curative properties when 

 administered to susceptible animals before or after inoc- 

 ulation with the living organism ? Does the serum of 

 immune animals possess the property of agglutinating 

 the organisms in relatively higher dilutions than the 

 serum of normal animals of the same species ? 



The majority of the bacteria may be identified with- 

 out resorting to such a detailed study of the biochemic 

 and pathogenic properties as given in the foregoing out- 

 line, but for some of the pathogenic bacteria it has been 

 necessary to apply all the known tests in order to defi- 

 nitely establish their identity. By means of such 

 detailed studies on related organisms, it has been possi- 

 ble to differentiate varieties whose characters are con- 

 stant, yet in general they are so closely related that it is 

 impossible from the clinical manifestations produced to 



