CHAPTER XL 



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 Culture 

 may be Ascertained — Dark Field Illumination — Facts Necessary to 

 Permit the Identification 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 estab- 

 lish its identity. Small portions of the pure culture are 

 taken upon the point of a sterile platinum wire and trans- 

 planted into the various culture-media. These sub-cultures 

 of the organism are then placed under suitable 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 of 

 the different media as shown by naked-eye (macroscopic) 

 examination as well as under a lens of low magnifying 

 power (microscopic); while equal importance must be given 

 to the chemical alterations produced by the bacteria in the 

 different media, and the influence of different reagents, 

 when added to the media, to show the presence of certain 

 metabolic products. In this manner the entire life history 

 of an organism, outside the animal body, may be ascertained. 



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