282 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



The pipettes, in their test tube sterilizing cases, are brought within easy 

 reach. Commencing at the left end of the front row of bottles proceed as 

 follows: Remove, without having the fingers come in contact with the bulb, 

 a 10 cc. pipette from its test tube case, get the soil and water in the first bottle, 

 (which is a 1-4 dilution of the bacteria in the field soil) thoroughly in motion 

 by shaking and while the mixture is still in motion fill the pipette. Pick up 

 the eight ounce dilution bottle which was directly behind the first bottle 

 taken, flame the cotton plug and remove it. While holding the plug in the 

 hand, blow out the 10 cc. mixture of soil and water from the pipette into the 

 90 cc. of water, replace the cotton plug, and set the bottle back in place. 



IM.ATK III. 



MakiiiK Hactcrial Dilutions. 



The pipette is dropped into a battery jar half full of water as it is hard to 

 clean if the soil is allowed to dry on the glass. The mixture just made is a 

 1-40 dilution of the bacteria in the field soil. Make the 1-40 bacterial dilu- 

 tions of the other samples in the same way. The bottle containing the 200 

 cc. of sterile water is treated exactly as though it contained soil, (Plate III.) 

 The V)ottles from which the dilutions have l)een made are })ut on a tray and 

 carried away. 



The bottles containing the 1-40 bacterial dilutions are each shaken for 

 ten seconds as vigorously as it is possible to shake them without wetting 

 the cotton plugs. When all have been shaken start over and shake each bottle 

 again. This is repeated until each bottle has been shaken 10 ten second 

 periods. The procedure followed in making: the 1-40 bacterial dilutions is 



