KOCH'S METHOD OF PREPARING PLATES. 65 



ferred to the moist chamber as rapidly as possible, so as to 

 avoid atmospheric contamination. To do this, one of the 

 benches is put on the top of the chamber. The top is then 

 lifted off and placed on the table near the leveller. The 

 plate is then quickly transferred to the bench. The latter 

 is lifted by its ends and placed at the bottom of the moist 



FIG. 19. Koch's levelling apparatus. 

 Hands shown in second position just as the 

 plate is lowered on to the ground glass surface. 

 By executing the transference of the plate from 

 the box in this way, the surface which was 

 undermost in the latter is uppermost in the 

 leveller, and thus, never meets a current of air 

 which might contaminate it. 



FIG. 20. 

 Esmarch's tube 

 for roll culture. 



chamber, the top of which is now replaced. Tubes b and 

 c are similarly treated, and the resulting plates stacked in 

 series on the top of a. The chamber is labelled and set 

 aside for a few days till the colonies appear in the gelatine 

 plates. The further procedure is of the same nature as 

 with Petri's capsules. 



3. Esmarch's Roll Tubes. Here the principle is that of 

 dilution as before. In each of three test-tubes \\ or ij 



5 



