200 STUDY OF THE PHYSIOLOGY OF BACTERIA 



For special kinds of bacteria other activities must be 

 determined (oxidation, nitrate and nitrite formation, action 

 of sulphur and iron bacteria, etc.)- 



The first nine activities are determined by inoculating 

 the different culture media already described and observ- 

 ing the phenomena indicated, making chemical tests where 

 necessary. 



APPEARANCE OF GROWTH ON DIFFERENT CULTURE 



MEDIA. 



In addition to those changes that are associated with the 

 manifestation of different physiological activities of bacteria, 

 many show characteristic appearances on the various cul- 

 ture media which are of value in their identification. 



Too much stress should not be laid on these appearances 

 alone, however, since slight variations, particularly in solid 

 media due especially to the age of the medium, may change 

 decidedly the appearance of a colony. This is true of 

 variations in the amount of moisture on agar plates. 

 Colonies which are ordinarily round and regular may assume 

 very diverse shapes, if there chance to be an excess of 

 moisture on the surface. 



Also in slope and puncture cultures on the various solid 

 media much variation results from the amount of material 

 on the inoculation needle and just how the puncture is 

 made, or the needle drawn over the slope. These variations 

 are largely prevented by the use of standard media and by 

 inoculating by standard methods. The Laboratory Com- 

 mittee of the American Public Health Association has pro- 

 posed standard methods for all culture media and tests and 

 for methods of inoculation, and these have been generally 

 adopted in this country for comparative work. 



Likewise the Society of American Bacteriologists has 

 adopted a standard "descriptive chart" for detailing the 

 characteristics of a given organism which includes the terms 

 to be used in describing the appearance on diflferent culture 

 media. This chart is inserted in this chapter. 



