LABORATORY WORK 299 



bacterium to be tested, so that the inoculation may be made from a 

 culture not over 24 hours old. Inoculate with a small amount of the 

 growth from the agar surface, the following : 



a. An agar slant, b. A gelatin stab. c. A" tube of plain 

 bouillon, d. A dextrose fermentation tube. e. A lactose fer- 

 mentation tube. /. Two milk tubes, one to be kept at 70° and 

 the other at 98 . g. Two potato 'tubes, one at 70 and one at 

 98. ° Allow the cultures to grow several days, examining each day. 

 For each species of bacterium make a careful record, noting es- 

 pecially the following points : 



Agar slant. Note the type of surface growth. 



Morphology. Stain and study with the microscope, noting 

 shape — formation of chains — spores — determine motility. 



Gelatin stab. Note liquefaction — needle growth — surface 

 growth — color. Compare the growth with the different types shown 



Fig. 72. 



1 2 3 4 5 6 "^l"* 



Types of Surface Elevation. 

 I. Flat. 2. Raised. 3. Convex. 4. Pulvinate. 5. Capitate. 6. Umbilicite. 



7. Umbonate. 



In figure 73, and determine with which each agrees. Note the 

 amount of elevation of the surface growth. 



Bouillon. Note turbidity — scum — sediment. 



Fermentation tubes. See below (No. 10). 



Milk tubes. Note at 70 and 98 the development of acid as 

 shown to litmus paper — curdling — separation of whey — appearance 

 of gas bubbles — subsequent softening of the curd, called digestion. 



Potato tubes. At 70 and 98 . Note color of growth — 

 abundance of growth — texture of growth — discoloration of potato. 



By such characters as above determined, different kinds of 

 bacteria are distinguished and described. For a complete descrip- 

 tion, more characters than those mentioned are necessary.* For 



* For more detailed description of special bacteria, see Conn's " Practical Dairy 

 Bacteriology." 



