186 BACTERIOLOGY 



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 environment 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 animals 

 may be immunized by the injection of sub-lethal doses 

 of dead or living cultures. Is a bactericidal immunity 

 induced by this means? Does the serum of immune animals 

 possess protective and curative properties when adminis- 

 tered to susceptible animals before or after inoculation 

 with the living organism? Does the serum of immune 

 animals possess the property of agglutinating the organ- 

 isms in relatively higher dilutions than the serum of normal 

 animals of the same species? 



The majority of the bacteria may be identified without 

 resorting to such a detailed study of the biochemic and 

 pathogenic properties as given in the foregoing outline, but 

 for some of the pathogenic bacteria it has been necessary 

 to apply all the known tests in .order to definitely establish 

 their identity. By means of such detailed studies on related 

 organisms, it has been possible to differentiate varieties 

 whose characters are constant, yet in general they are so 

 closely related that it is impossible from the clinical mani- 

 festations produced to state definitely which particular 

 variety of organism is responsible for the conditions. This 



