TECHNIC BACTERIOLOGICAL EXAMINATION OF SOILS. 299 



Table VIII. 



All of the bottles were left standing on the laboratory table for 24 hours. 

 They were then weighed again. Those with cotton plugs had lost about 1.5 

 grams on standing, and those with no plugs had lost more. 



If sterilization in the autoclave did not change the volume of water in the 

 dilution bottle the practice should be discontinued in soil work as the bottles 

 would have to stand on the laboratory tables for varying lengths of time. 



Water could be more accurately added to the dilution bottles with an 

 automatic pipette than it can be with a graduated cylinder. Automatic pipettes 

 that can be easily sterilized and connected directly to the special tank for 

 sterile water are being investigated, but cannot at this time be recommended 

 to graduated cylinders which can be made absolutely sterile. 



Shaking Dilution Bottles 



Stress has been laid on the manner of holding and the manner of shaking 

 •the soil and water mixtures. The following make it necessary to emphasize 

 shaking. 



1. Variations in manner different individuals shake up materials. 



2. Variation in the ease with which colonies of bacteria are disintegrated 

 by shaking. 



3. Variation in nature of different soils. 



Rather than recommend shaking a certain length of time in a specified 

 make of shaking machine the technic of shaking is given in such a way that any 

 accidental variations introduced by different individuals will have little effect 

 on the result*. 



