60 A MANUAL OF BACTERIOLOGY 



heated to 40 C. or 55 C. respectively, so as to melt 

 the medium in each tube. The tubes are then care- 

 fully inoculated with a mere trace of the original 

 fluid. The cotton-wool plugs are replaced, and the 

 tubes rolled about so as to distribute the microbes 

 throughout the media. The contents of the tubes 

 are quickly poured into the lower portion of the 

 same number of Dr. Petri's double dishes (Fig. 23 B) 

 or glass plates (Fig. 23 A). The dishes or plates 

 (which should have been previously sterilised) are 

 then placed in a damp chamber (see Fig. 22). The 

 damp chamber, with its contents, are removed to an 



FIG. 23. APPARATUS FOR PLATE-CULTIVATION. 

 A, Glass Bench with'Plates. B, Petri's Double Dish. 



incubator, and remain there for several days at 

 about 23 C., or higher if agar-agar is used (i.e. 

 according to the temperature required for the 

 growth of the microbes). 



In a few days or so each species will have 

 started a separate growth or colony in different 

 parts of the solidified plate of nutrient gelatine, or 

 agar-agar. The individual colonies are recognisable 

 according to certain macroscopical appearances, such 

 as colour, shape, liquefaction or non-liquefaction of 

 the medium, and the size of the colonies. By plate- 

 cultivation the different species of microbes (i.e. in 



