196 BACTERIOLOGY. 



itself. Record the manner in which the culture changes 

 in its appearance on successive days. 



Agar-stab Inoculations. Observe the nature of the 

 growth in an agar-agar-stab inoculation. Note whether 

 the growth is most voluminous at or near the surface 

 or in the depth of the stab. If the organism produces 

 pigment, note whether the pigment-formation is most 

 marked at or near the surface or at the bottom of the 

 stab. Record the alterations that are observed on sev- 

 eral successive days. 



Gelatin-stab Inoculations. Observe the nature of the 

 growth in a gelatin-stab inoculation. Is the growth 

 most voluminous at or near the surface or at the bottom 

 of the stab ? Note the general character of the growth 

 on the surface, especially as to its contour, extent, and 

 color. Note the character of the growth in the stab. 

 Is it continuous along the whole line of inoculation, or 

 is it confined to isolated areas ? If the organism has 

 the property of liquefying gelatin, note carefully the 

 manner in which the liquefaction proceeds. How soon 

 does liquefaction begin, and in what length of time is a 

 tube of gelatin completely liquefied? 



Potato Culture. Observe the nature of the growth on 

 potato. This is an important differentiating medium, 

 since some organisms grow very sparingly or without 

 producing a visible growth. Other organisms grow 

 very characteristically. Some organisms have the prop- 

 erty of breaking up the starch of the potato into sim- 

 pler compounds. This is sometimes manifested by the 

 formation of gas. Many of the chromogenic bacteria 

 find the potato a most suitable pabulum on which to 

 form their pigment, the pigment formed on this medium 

 having at times an especial brilliancy. Note in detail 



