CHAPTER XI. 



Systematic study of an organism — Steps necessary in identifying 

 an organism as a definite species. 



After isolating an organism by the plate method, 

 considerable work is necessary in order to establish its 

 identity as a definite species. 



It must possess certain morphological and cultural 

 peculiarities, which must be constant under constant con- 

 ditions. 



Its form at certain stages must always be the same. 

 Its ability or inability to produce spores must not vary 

 under proper conditions. Its growth upon the different 

 media under constant conditions of temperature must 

 always present the same outward appearances. The 

 reactions given by it to the media in which it is growing 

 must follow a fixed rule. Its power to produce liquefac- 

 tion of the gelatin, or to grow upon it without bringing 

 about this change, must always be the same. Its motility 

 or non-motility must be determined. Its production of 

 certain chemical products must foe detected by chemical 

 analysis. Its behavior toward oxygen — i. e., does it re- 

 quire this gas for its growth ? is this gas an indifferent 

 factor? or by its presence are the life processes of the 

 organism checked? — must be determined. Its behavior 

 under varying conditions of temperature and under the 

 influence of different chemical bodies as well as its growth 

 in media of different reactions are to be studied. The 

 property of producing ferm^tation with the libera- 



