PLATE CULTURES. 23 



large number of bacilli to be present, a further dilution 

 can be made from tube No. 2. 



(d) Heat the tops of the inoculated tubes to assure 

 thorough sterilization, and then permit them to cool. 



(e) Remove the plugs and carefully pour the gela- 

 tine into sterilized Petri dishes, causing the gelatine to 

 spread thoroughly over the plate surface. 



(/) Set the gelatine by placing the plates on blotting 

 paper moistened with cold water, and then place in 

 incubator at 20°C. 



Examine at the end of 24, 48 and 72 hours, noting 

 the character and number of colonies, and the presence 

 of other species of bacteria. 



Esmarch roll tubes may be prepared instead of plates, 

 by spreading the liquefied gelatine over the sides of the 

 tubes and setting the gelatine rapidly by revolving the 

 tubes on ice. 



5. Make cultures of Staphylococcus pyogenes aureus, 

 Staphylococcus pyogenes albus and Bacillus pyocyaneus 

 in agar, potato and gelatine (stab) tubes. 



6. Make cultures of Streptococcua pyogenes in agar, 

 gelatine (slope) and broth tubes. 



Examine these cultures day by day, noting the gen- 

 eral characters of growth. 



