58 METHODS OF CULTIVATION OF BACTERIA 



For accurate work it will be found convenient to carry out 

 the dilutions in definite proportions. The following is the pro- 



FlG. 18. Koch's levelling apparatus for use in preparing plates. 

 Hands shown in first position for transferring sterile plate from iron 

 box to beneath bell jar, where it subsequently has the medium poured 

 out upon it. 



cedure which we .have found very serviceable : In a number of 

 small sterile test-tubes '95 c.c. sterile water is put. To the first 



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 con- 

 taminate it. 



tube we add '05 c.c. of the bacterial mixture. The contents of 

 the tube are well shaken up, and the pipette is sterilised by 



