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. 



