130 BACTERIOLOGY. 



the distribution of the organisms and the better the 

 results. The loop is then again sterilized and three 

 of its loopfuls are passed, without touching the sides of 

 the tube, from " the original " into tube No. 2, where 

 they are carefully mixed. Again the loop is sterilized, 

 and again three dips are made from tube No. 2 into 

 tube No. 3. This completes the dilution. The loop is 

 now sterilized before laying it aside. 



FIG. 24. 



Levelling tripod with glass cooling chamber for plates. 



During this manipulation, which must be done 

 quickly if agar-agar be employed, the temperature of 

 the water in the bath in which the tubes stand should 

 never be lower than 39 C., and never higher than 

 43 C. If it falls below 38 C., the agar-agar solid- 

 ifies, and can only be redissolved at a temperature 

 that would be destructive to the organisms which may 

 have been introduced into the tubes. This is not of 

 so much moment with gelatin, since it may readily be 



