CULTURE METHODS 



plug, and heat the mouth of the tube in the Bunsen flame, inoculate 

 with a platinum loop of a liquid culture, or a trace of any semi-solid 

 culture, or other desired material. After inoculation distribute the 

 organisms evenly, allowing the fluid to flow gently backwards and 

 forwards, avoiding contact with the cotton plug, as too much agitation 

 causes air-bubbles to form. The tube is held between the thumb 

 and first finger of the left hand, while the cotton plug is placed 

 between the first joints of the first and second fingers of the same 

 hand. This is now known as the original tube, and marked c O. 1 



3. Take another tube of gelatine, remove the plug, placing it 

 between the second and third fingers of the left hand, sterilize the 

 mouth of the tube, place it alongside the original tube, and with a 

 sterilized platinum loop transfer three loops of the gelatine in the 

 original tube into the second tube. Replace the plug in the original 

 tube and set on one side. The second tube is known as No. 1 Dilu- 

 tion, and marked ' I.' 



4. The third sterilized tube of gelatine is inoculated with three 

 platinum loops from the second tube, or No. 1 Dilution, in the same 

 manner, and is known as No. & Dilu- 

 tion, and marked ' II.' (For marking 



the tubes for future identification, 

 yellow or blue coloured pencils for 

 writing on porcelain, metal, or glass, 

 will be found very convenient.) 



5. Three sterilized glass plates are 

 now removed from the plate box, 

 placed one above the other on the 

 ground glass plate of the plate culture 

 apparatus (see Fig. 11), and the con- 

 tents of the above tubes poured in 

 order on the plates. When the gela- 

 tine is thoroughly set, the plates are 



, T 111 i 1 1 FIG. 11 Koch's Plate Culture Apparatus. 



placed on glass benches one above the 



other, the original plate being at the bottom in a plate culture dish. 

 Instead of using plates, it is simpler to pour the gelatine into sterilized 

 Petri-dishes. The prepared plates or Petri-dishes can be placed in the 

 incubator at 22 C., or left to develop at room temperature ; as a rule 

 only two of the plates are fit for future observation the original 

 generally containing too many colonies. When finished, sterilize the 

 platinum wires, and place the empty tubes in the disinfecting solu- 

 tion. A piece of filter paper, with the number and date, is sometimes 

 placed on the glass benches below the plates. 



