TECENIQUE OF MAKING PLATES. 83 



distribution of the organisms and the better the results. 

 The "oese" 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 "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 



