230 METHODS OF CULTIVATION 



elevating the bottom of the tube, pour the liquefied 

 medium into the Petri dish, to form a thin layer. 

 Remove the mouth of the tube and close the' 'plate/* 

 If the medium has failed to flow evenly over the bottom 

 of the plate, raise the plate from the levelling platform 

 and by tilting in different directions rectify the fault. 



9. Pour plates No. 2 and No. 3, in a similar manner, 

 from tubes Nos. 2 and 3. 



10. Label the plates with the distinctive name or 

 number of the inoculum, also the date; the number of 

 the dilution having been previously indicated (step 3). 



11. Place in the cool incubator for three or more 

 days, as may be necessary. 



In this way colonies may be obtained quite pure and 

 separate from each other. 



In plate No. i, probably, the colonies will be so 

 numerous and crowded, and therefore so small, as to 

 render it useless. In plate No. 2 they will be more 

 widely separated, but usually No. 3 is the plate reserved 

 for careful examination, as in this the colonies are usu- 

 ally widely separated, few in number, and large in size. 



Agar plates are poured in a similar manner, but the 

 agar must be melted in boiling water and then allowed 

 to cool t045C. or42C. in a carefully regulated water- 

 bath before being inoculated, and the entire process 

 must be carried out very rapidly, otherwise the agar 

 will have solidified before the operation is completed. 



NOTE. In pouring plates, since tube No. i (for the first dilu- 

 tion) rarely gives a plate that is of any practical value it is fre- 

 quently replaced by a tube of bouillon or sterile salt solution, and 

 in such case plate No. i is not poured. 



Surface Plates. 



This method of pouring what may be termed " whole " 

 plates (since colonies may appear both on the surface 

 and in the depths of the medium) is essential to the 

 accurate study of the formation of colonies under 



