BIOLOGY OF CLOSTRIDIUM WELCHII 385 



On thickly seeded glucose-liver agar plates, abundant gas 

 production occurs, while on plates containing only a few colonies 

 no gas usually occurs; but occasionally two or three colonies 

 on glucose-liver-agar plates will develop sufficient gas to cause 

 a bubble to appear covering the entire plate under the paraffin. 

 This bubble, if punctured, burns with the blue flame characteristic 

 of hydrogen. Gas formation frequently fails to occur in deep 

 glucose-liver agar stab cultures, when only two or three colonies 

 develop in the lower part of the medium. 



Nutrient agar of + 1 reaction with 1 per cent glucose or lactose 

 causes a rapid and luxuriant growth with more abundant and 

 speedy gas formation than occurs on plain nutrient agar without 

 sugar. The odor of plain agar cultures is not putrescent or 

 characteristic. The odor of sugar agar cultures resembles that 

 of sour, stale glue, a condition more pronounced with some 

 strains than others. 



b. Colonies. Colonies of Clostridium Welchii do not develop 

 in plain meat extract agar unless all the oxygen is first removed 

 and strict anaerobic methods employed in the plating. The 

 more strictly anaerobic the conditions employed the larger the 

 colonies as shown by the fact that the colonies in stab nutrient 

 or sugar agar, are very much larger at the lower part of the needle 

 track. In fact when agar stab cultures are inoculated (after 

 sufficient steaming to dispel the air) growth appears most abun- 

 dant at the bottom of the stab, ceasing to develop some distance 

 below the surface, according to the degree of the anaerobiosis. 



Colonies of Clostridium Welchii in plain and sugar agar are 

 opaque white, grayish white, or even of a brownish white color 

 by transmitted light, sometimes with a central darker dot, the 

 opacity of the color depending upon the thickness of the colony. 

 The dark center appears in all media in which the organism 

 sporulates. 



Young cultures vary in size from 0.5 to 1 mm. in diameter, 

 but frequently increase to diameters of 2 to 3 mms. or even 

 larger. The colonies in plain agar are very minute pin points 

 with fuzzy edges and with a zone around them resembling a 

 halo. A dark center appears in the colony after ten to twelve 



