TECENIQUE OF MAKIIfG PLATES. 83 



distribution of the organisms and the better the results. 

 The " oese " is then again steriHzed, 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 "oese" is sterilized 

 and again three dips are made from tube 2 into tube 3. 

 This completes the dilution. The "oese" is now steril- 

 ized before laying it aside. 



Fig. 11. 



During this manipulation, which must be done quickly 

 if agar-agar is employed, the temperature of the water in 

 the bath in which the tubes stand should never get lower 

 than 39° C, and never higher than 43° C. If it falls 

 too low, below 38° C, the agar gelatinizes, and can 

 only be redissolved by a temperature which would be 

 destructive to the organisms which may have been in- 

 troduced into the tubes. This is not of so much 

 moment with gelatin, as it may readily be redissolved 



