232 METHODS OF CULTIVATION 



spreader all over the surface of the gelatine then go 

 on in like manner to the third plate in the series. 



7. Sterilise the spreader. 



8. Label and incubate the plates. 



After incubation, plate No. i will probably yield an 

 enormous number of colonies; plate 2 will show fewer 

 colonies, since only those bacteria adhering to the rod 



FIG. 127. Spreading surface plate. 



after rubbing over plate i would be deposited on its 

 surface, and by the time the rod reached plate 3 but 

 very few organisms should remain upon it. So that 

 the third plate as a rule will only show a very few 

 scattered colonies, eminently suitable for detailed 

 study. 



(b) Agar Surface Plates. 



1. Liquefy three tubes of nutrient agar nutrose 

 agar or the like. 



2 . Pour each tube into a separate Petri dish and allow 

 it to solidify. 



3 . When quite solid invert each dish, raise the bottom 

 half and rest it obliquely on its inverted cover (Fig. 128) 

 and place it in this position in an incubator at 60 C. 

 for forty- five minutes (or in an incubator at 42 C. for 



