ANAEROBIC CULTURE METHODS 155 



ment is set free as a useless excretion, may be excreted as a 

 colored body or as a colorless substance which becomes 

 oxidized upon exposure to the air. Individual cells are 

 colorless and may cease to form pigment, e.g., B. prodigiosuSj 

 B. ruber, B. indicus. 



Parachrome bacteria. The pigment is an excretory prod- 

 uct but is retained within the cell, e.g., B. violaceus. (Bei- 

 jerinck.) 

 According to their temperature relations, into: 



Pecilothermic (poikilothermic) bacteria: adaptability to 



temperature of environment; 

 Stenothermic bacteria: a very narrow temperature 



range (strict parasites); 



Eurythermic bacteria: a very wide temperature range 

 (metatrophic bacteria), often 30 between maximum 

 and minimum temperatures. 

 According to their optimum temperature, into: 



Cryophilic (psychrophilic, term 



used chiefly for water organ- Min. Opt. Max. 



isms) bacteria C. 15 C. 30 C. 



Mesophilic bacteria (includes 



pathogenic bacteria) 15 C. 37 C. 45 C. 



Thermophilic bacteria 45 C. 55 C. 70 C. 



ANAEROBIC CULTURE METHODS 



The cultivation of strict anaerobes is accompanied by 

 certain technical difficulties arising from the necessity of 

 removing all traces of oxygen from the medium and from 

 the atmosphere to which this medium is exposed. It is, 

 therefore, necessary to employ special apparatus or special 

 methods for their cultivation. 



The recent investigations of Tarrozzi, which have been 

 confirmed by others, seem to show that oxygen does not exert 

 any direct harmful effect on anaerobic organisms, but that 

 the presence of free oxygen prevents the medium furnishing 



