70 CULTIVATION OF AEROBIC MICRO-ORGANISMS 



The wire must not be exposed to the air any longer than is necessary for 

 it to cool otherwise it may be contaminated by dust, and it is because it cools 

 more quickly that a fine wire is most generally used. 



3. Pick up the material to be sown on the needle, and transfer it to the 

 medium to be inoculated. 



4. When the culture is sown, heat the platinum wire to redness to destroy 

 any organisms which may still be present on it. 



This is particularly important when dealing with pathogenic micro-organisms. 

 If the needle be not sterilized immediately, it will soil the bench and anything else 

 it may touch. 



C. Glass needles. 



Draw out a piece of glass rod in the same way as the tubing was drawn 

 out when making Pasteur pipettes. Then with a glass-cutter, [file, or piece 

 of carburundum pencil] divide the fine part squarely in the middle. In this 

 way needles of any degree of fineness can be made. 



These needles are not so easy to handle as a platinum wire, but have the 

 advantage of being rigid. They are useful for sowing deep stab cultures in 

 gelatin. 



Flame the needles immediately before using them. 



SECTION II. THE METHODS OF SOWING CULTURES. 



A culture medium may be sown from another culture, or with water, dust, 

 blood or other material. The method of collecting material differs of course 

 according to the source whence it is derived and this will be dealt with 

 later (Chap. XII.) but the technique of sowing cultures is not affected by 

 these variations. Assume for the moment that a sub-culture is to be sown 

 from an already existing culture, and take as an example a broth culture of 

 the anthrax bacillus. 



The process may be divided into three stages. 



(i) The opening of the tube from which the culture material is to be taken. 



(ii) The removal of the material. 



(iii) The sowing of the new medium. Here several alternatives present 

 themselves. It may be required to sow 



(a) Broth, or other liquid medium. 



(6) Stroke cultures on agar, gelatin, serum or potato. 



(c) Gelatin stab cultures. 



(It is sometimes required to sow single colonies for isolating organisms 

 in pure culture : this will be dealt with separately in a later chapter.) 



These various problems will now be considered seriatim. 



A. Method of sowing a liquid medium. Broth may be taken as a type of 

 liquid media. 



1. Take a tube of sterile broth and the tube containing the organism. 

 Flame the plugs of both tubes to burn off the dust which has collected on 

 them. Loosen the plugs by screwing them round with the thumb and index 

 finger of the right hand, at the same time slightly withdrawing them. 



2. Place both tubes side by side in the left hand, holding them as nearly 

 horizontally as possible. The bottom of the tubes should rest in the hollow 

 of the hand, their upper parts being grasped between the thumb, index and 

 middle fingers. 



3. Take a platinum loop between the index and middle finger of the right 

 hand, and sterilize it as already described. 



4. While the needle is cooling, take the plug, which has already been 



