' SHAKE ' CULTURES 75 



is not strictly aerobic, but may grow either in the presence 

 or absence of oxygen, and is thus a facultative anaerobe. 



Again, we have differences as to the character of the 

 growth both along the line of puncture and on the surface. 

 The surface growth may be composed of a piled-up mass at 

 the point where the rod entered the gelatine, or the growth 

 may form a layer which entirely covers the surface of the 

 medium. The growth along the line of inoculation in the 

 depth differs very much in different species. We may have 

 a number of spherical colonies, or we may have little tufts 

 forming moss-like projections from the line of puncture. 

 The characters of the liquefying organisms are very cha- 

 racteristic. The liquefaction may take place all along the 

 line of inoculation, forming a long narrow funnel of liquefied 

 gelatine, or we may have a broad funnel, or a wide cup-like 

 cavity of liquefied medium. 



' Shake ' Cultures. — A tube of gelatine or agar medium is 

 liquefied by heating the tube in a beaker of hot water, 

 which is then slowly cooled until the temperature of .the 

 water is 40° C. The medium is then inoculated with 

 the organism under examination. The plug is replaced, 

 and the tube well shaken to distribute the organisms 

 evenly through the medium, care being taken not to allow 

 any of the gelatine to touch the cotton-wool plug. The 

 contents of the tube are allowed to set in cold water. On 

 incubating the tube at the room or higher temperatures, as 

 the case may be, many organisms will be found to give 

 rise to the formation of gas, the bubbles of which will 

 become larger in size as growth increases. 



Culture of Anaerobic Bacteria. — In addition to the method 

 of studying anaerobic organisms by means of ' stab ' cul- 

 tures, many methods have been employed from time to 

 time, which depend upon the withdrawal of the oxygen 

 from the culture-tubes. 



