82 ISOLATION OF AEROBIC MICRO-ORGANISMS 



Let the agar set firmly. 



2. Take up a trace of the material under investigation on the wire, raise 

 the cover of the Petri dish, and without recharging the needle make a series 

 of parallel strokes on the agar each a few millimetres distant from the other. 



As the needle is drawn over the agar the material on it is transferred to 

 the latter, and it is obvious that after the wire has been drawn across the 

 agar three or four times the number of organisms left along the line of any 

 stroke will be but few in number. 



3. Incubate the plate at 37 C. The colonies which develop along the 

 first strokes will be very numerous, but will be fewer and fewer along the 

 later ones. 



B. Surface cultures. 



1, Classical method. This method of isolation may be illustrated by 

 describing it as it would be used with sloped serum, but the method is the 

 same for agar, potato, etc. 



Apparatus required. 1. A stout platinum wire flattened at the end. 



2. Three tubes of sloped solidified serum. 



Technique. 1. Take up a trace of the material under investigation on 

 the wire. 



2. Remove the plug from one of the serum tubes, dip the needle into the 

 tube and smear the whole surface of the medium, commencing below and 

 working towards the mouth (tube 1). 



3. Without recharging the needle sow a second tube of serum in the same 

 way (tube 2). 



4. Sow the third tube similarly, again without recharging the needle 

 (tube 3). 



5. Incubate the tubes at 37 C. 



As the result of drawing it over the surface of the serum, the needle is 

 gradually wiped clean of the organisms with which it was charged and 

 which have been deposited on the serum. Tube No. 1 will grow numerous 



confluent colonies, but tubes No. 2 and No. 3 

 will grow fewer colonies and some of them will 

 be well isolated. The discrete and isolated 

 colonies on the latter tubes can be used for 

 further investigation. 



2. Veillon's method. 1. Take a trace of the 

 material on a platinum wire. 



2. Without recharging it, dip it into the water 

 of condensation -at the bottom of 4 or 6 agar 

 tubes. 



3. Replug the tubes and sow the surfaces of 

 the agar by running the water of condensation 

 over them. Incubate the tubes in the vertical 

 position. 



3. Chantemesse's method. This is useful for 

 ?IG> 7 bylrSn'rm e f thod aniS the purpose of isolating organisms present in 



stools. 



1. Dilute a trace of the material in several cubic centimetres of distilled 

 water. 



2. Dip a sterile badger-hair pencil into this highly diluted material. 



3. Brush the surface of a series of 5 or 6 agar plates (prepared in Petri 

 dishes as described above under A, p. 8D without recharging the brush. 



