76 FRED W. TANNER 



Gelatin colonies \ 



All cultures gave abundant growth on this medium. The 

 non-liquefiers grew on the surface and often spread over a large 

 area. Fluorescence was very evident on this medium. The 

 liquefying cultures gave large saucer-shaped colonies which were 

 filled with a flocculent growth. 



Gelatin stab 



The medium used in this test was made from Gold Label 

 French gelatin. Twelve per cent of gelatin was added to plain 

 peptone bouillon. The medium was put into test tubes to the 

 depth of about 7 cm. Inoculations were made into these tubes 

 by means of a platinum needle, stabbing to the bottom of the 

 test tube. The cultures were incubated for thirty days at 

 20°C., as recommended on the descriptive chart of the Society 

 of American Bacteriologists. 



At the end of thirty days 59 of the cultures had liquefied the 

 gelatin. The gelatin cultures of the other 41 were left in the 

 incubator for over fourteen months. During that time strains 

 7, 19, 67 and 83 hquefied the medium. With strains 7 and 19, 

 the liquefaction took place at the end of three months. Strains 

 67 and 83 required about six months for this change. The other 

 37 strains did not liquefy gelatin in fourteen months when 

 kept at 20 °C. The tubes were fitted with rubber caps to pre- 

 vent evaporation. In determining the group number, only 

 those strains were considered as liquefiers which produced lique- 

 faction in thirty days. In all cases the growth seemed to be 

 best at the surface, although it often extended throughout the 

 tube down into the medium along the line of inoculation. At 

 the end of six or seven days, fluorescence was noticeable. This 

 soon extended throughout the tube, the greatest amount being 

 at the surface. 



The characteristic of liquefaction is recognized as an impor- 

 tant one in separating bacteria. The possession of a proteo- 

 lytic enzyme sharply separates a strain from those which do 

 not possess this enzyme. The method for determining this 



