78 APPLIED BACTEEIOLOGY 



cultures are very various. In the case of non-liquefying 

 organisms, the growth may be entirely on the surface or 

 only in the depth. In the first case, the organism is aerobic 

 — that is, it requires oxygen for its growth, and will only grow 

 in presence of this gas '; in the second case, the organism 

 is anaerobic, in which case it cannot grow in the presence 

 of oxygen or air, and consequently does not grow upon the 

 surface of the culture medium or along the upper portion of 

 the line of puncture. 



The growth, again, may grow both on the surface and 

 also along the line of puncture. In this case the organism 

 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 



