64 ESSENTIALS OF BACTERIOLOGY. 



The first tube is called original. From this three drops (taken 

 with the looped platinum rod) are placed in a second tube, the 

 rod being shaken somewhat in the gelatine or agar ; this is 

 labeled first dilution (a colored pencil is useful for such markings). 



FIG. 24. 



Manner of holding tubes for inoculation : a, tube with material ; b, tube to be 

 inoculated ; c, cotton plugs. 



From the first dilution three drops are taken into a third tube, 

 which becomes the second dilution. 



The plugs of cotton must be replaced after each inoculation, 

 and during the same must be carefully protected from contami- 

 nation. 



