TECHNIQUE 



87 



than 50 per cc, it would be desirable to use i cc. quantities for 

 plating which would give about 50 colonies in the plate. 



The thorough mixing of the sample before making the dilutions 

 is of the greatest importance, likewise the thorough mixing of 

 each dilution before taking out the quantity to be'plated. Each 



Fig. 23. — Types of growth in stab cultures. A, Non-liquefying, i, Filiform 

 (Bacillus coli); 2, beaded (Streptococcus pyogenes); 3, echinate (Bacterium acidi 

 lactici); 4, villous (Bacterium murisepticum); $, arborescent (Bacillus mycoides). 



B, Gelatin liquefying. 6, Crateriform (Bacillus vulgare, 24 hr.; 7, napiform 

 (Bacillus subtilis, 48 hr.); 8, infundibuliform (Bacillus prodigiosus); 9, saccate 

 (Microspira finkleri); 10, stratiform (Pseudomonas fluorescens). — (McFarland, 

 ajter Frost.) 



test should be made in triplicate, taking up the i cc. amounts 

 for making the dilutions with three different clean sterile pipettes. 

 It is preferable to use a new pipette for each dilution. If it is 

 not convenient to have on hand a sufficient number of clean 

 sterilized pipettes, the pipette in use must be thoroughly 



