CHAPTER VI. 



THE CULTIVATION AND ISOLATION OF ANAEROBIC 

 MICRO-ORGANISMS. 



Introduction. 



Section I. The methods of abstracting air from culture media, p. 87, 



1. By boiling, p. 87. 2. By displacing the air with some inert gas, p. 88. 3. By 

 absorbing the oxygen, p. 89. 4. By the use of a vacuum, p. 90. 

 Section II. The cultivation of anaerobic organisms, p. 92. 



1. Liquid media, p. 92. 2. Solid media, p. 99. 

 Section III. The isolation of anaerobic organisms, p. 101. 



1. Plate method, p. 101. 2. Tube method, p. 103. 

 Section IV. Vacuum incubators, p. 104. 



SOME organisms grow equally well under both aerobic and anaerobic con- 

 ditions, others grow only when the medium in which they are sown contains 

 no trace of free oxygen ; the former are known as the facultative anaerobes, 

 the latter as the strict anaerobes. The cultivation of the strictly anaerobic 

 organisms is accompanied by certain technical difficulties arising out of the 

 necessity for removing all traces of air from the culture medium in which they 

 are sown. The culture media are the same for the two classes, but for the 

 strictly anaerobic organisms special forms of culture apparatus and special 

 methods are required, and it is to a description of these that the present 

 chapter is devoted. 



The recent investigations of Tarrozzi, which have been confirmed by 

 Wrzosek, Guillemot, Ori and others, seem to show that oxygen does not 

 directly exert any harmful influence on anaerobic organisms, but that the 

 presence of free oxygen prevents the media furnishing the nutritive 

 substances necessary for anaerobic life. 



Anaerobic organisms can in fact, as Tarrozzi has shown, be grown in 

 presence of the oxygen of the atmosphere by simply adding pieces of animal 

 tissue or some reducing agent to the culture media (vide infra). 



SECTION I. METHODS OF ABSTRACTING AIR FROM CULTURE 



MEDIA. 



1. By boiling. 



can be expellee 

 must be boiled f 

 and then be cooled rapidly away from the air. 



Gases dissolved in a liquid can be expelled by boiling. To expel all the 

 air from a culture medium it must be boiled for 20 minutes to half an hour, 



