CHAPTER XI. 



Systematic study of an organism Points to be considered in determin- 

 ing the morphologic and biologic characters of a culture Methods 

 by which the various biologic and chemical characters of a cul- 

 ture may be ascertained Facts necessary to permit the identifi- 

 cation of an organism as a definite species. 



AFTER isolating an organism in pure culture by the 

 plate method, considerable work is necessary in order to 

 establish its identity. Small portions of the pure cult- 

 ure are taken upon the point of a sterile platinum wire 

 and transplanted into the various culture-media. These 

 sub-cultures of the organism are then placed under suit- 

 able conditions of temperature and environment, and 

 examined from day to day to note the alterations that 

 occur in the different media. In the systematic study 

 of an organism no one character can be relied upon to 

 the exclusion of others. It is necessary to note the 

 microscopic appearance of the individual organism and 

 its behavior toward different staining solutions and 

 other reagents ; in addition it is necessary to note the 

 gross appearance of the culture on the different media 

 as shown by naked-eye (macroscopic) examination as 

 well as under a lens of low magnifying power (micro- 

 scopic) ; while equal importance must be given to the 

 chemical alterations produced by the bacteria in the dif- 

 ferent media, and the influence of different reagents, 

 when added to the media, to show the presence of cer- 

 tain metabolic products. In this manner the entire life 

 history of an organism, outside the animal body, may 

 be ascertained. 



173 



