90 BACTERIOLOGY. 



tube. After this they may be retained in the upright 

 position without fear of the agar-agar slipping down. 

 We have followed this process for several years with 

 entire satisfaction. 



In all these processes, if the dilutions of the num- 

 ber of organisms have been properly conducted, the 

 results will be the same. The original plate or tube, 

 as a rule, will be of no use because of the great number 

 of colonies contained in it. Plate or tube No. 2 may be 

 of service, but plate or tube 3 will usually contain the 

 organisms in such small numbers that the colonies 

 originating from them will have nothing to prevent 

 their characteristic development. 



For reasons of economy, the "original," tube 1, 

 is sometimes substituted by a tube containing normal 

 salt solution (0.6 to 0.7 per cent, of sodium chloride 

 in water), which is thrown aside as soon as the dilu- 

 tions are completed and only plates or tubes 2 and 3 

 are made. 



