194 BACTERIOLOGY 



tendency to spread over the surface of the medium? Is 

 it smooth or rough, moist or dry, glistening or dull in 

 character? If the organism forms pigment, note whether 

 the pigment is confined to the area of growth or whether it 

 extends into the medium 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 several 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 liquefy- 

 ing gelatin, note carefully the manner in which the lique- 

 faction 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 differential medium, since 

 some organisms grow upon it very sparingly or indeed 

 almost invisibly. Other organisms grow very character- 

 istically. Some organisms have the property of breaking 

 up the starch of the potato into simpler compounds. This 

 is sometimes accompanied by the evolution of gas. Many 



