DESGBIBING AN ORGANISM. 229 



activities. Variations in virulence, and the probable 

 causes to which they are due. Can they be produced 

 artificially and at will ? 



15. The detection of specific, toxic, and immunizing 

 products of growth. 



16. Its behavior when exposed to the influence of 

 blood-serum of animals immunized from it; also its 

 behavior when mixed with serum from an animal in 

 the acute stage of infection resulting from it. Are the 

 relations between the organism and the serum constant 

 and specific ? 



