20 LABORATORY EQUIPMENT 



The unit for measuring the amount of bacteria grown upon a solid 

 medium is represented by a standard sized loop. This platinum loop takes 

 up about 2 mg. of bacterial substance. It is prepared as explained in Fig. 

 2. If smaller amounts of bacteria are used, dilutions must be made. 



For instance. 1/4 of a loopful of bacteria is desired; i loopful is suspended in i c.cm. 

 of saline and 3 c.cm. of saline added. As a result, i c.cm. of this emulsion contains 1/4 

 of a loopful of bacteria. If 1/16 of a loopful is necessary i c.cm. of the above dilution 

 is added to 3 c.cm. of saline, thus making i c.cm. of this last mixture contain 1/16 

 of a loopful of bacteria. 



