198 BACTERIOLOGY. 



ma, production of gas in media containing different car- 

 bohydrates, or the reducing power of the organism on 

 aniline dyes, etc. 



Influence of External Agencies. Note the vitality of 

 the organism under the influence of various physical and 

 chemical agents. Determine the temperature at which 

 it thrives best, as well as the lowest and highest tem- 

 peratures at which growth is possible. Determine the 

 thermal death-point of the organism by subjecting it to 

 various degrees of temperature from 55 to 75 0. for 

 ten minutes. Determine its resistance to drying ; to 

 the influence of light ; to the influence of germicidal 

 substances. Determine the influence of different gases 

 upon the growth of the organism, such as hydrogen, 

 nitrogen, or carbon dioxide. Determine the chemical 

 reaction of the culture-media best adapted for its 

 growth. 1 



BIOCHEMIC CHARACTERS. If the organism exhibits 

 chromogenic properties, ascertain whether the pigment 

 is intra- or extracellular. Ascertain under what condi- 

 tions of temperature, reaction, and constitution of media, 

 or under what atmospheric conditions this function is 

 best exhibited. Note the influence of different reagents 

 upon the pigment, such as chloroform, ether, alcohol, 

 water, acids, or alkalies. Note whether the organism 

 exhibits photogenic properties, and if so, ascertain what 

 conditions are most suitable for the manifestation of this 

 phenomenon. 



Ascertain whether or not the organism produces en- 

 zymes. Does it manifest a proteolytic function, as shown 



1 For more detailed description of the variations in the character 

 of the macroscopic and microscopic appearance of the cultures in the 

 different media, the student is referred to Chester s Determinative 

 Bacteriology and Eyre's Bacteriologic Technique. 



