METHODS OF SOWING CULTURES 



71 



loosened, out of the tube containing the organism with the thumb and index 

 finger of the right hand. Hold the plug between the thumb and first finger. 

 5. Introduce the platinum wire into the tube, being careful not to let it 

 touch the sides of the mouth. Take up a drop of the culture fluid in the loop, 

 and withdraw the latter from the tube (fig. 56). Flame the mouth of the 



A 



FIG. 56. Method of sowing a liquid medium. 



tube at once to destroy any organisms which may have settled on it during 

 the process, and replace the plug as quickly as possible. 



6. Take the plug out of the other tube, dip the loop into the broth, and 

 after withdrawing it flame the mouth of the tube and replace the plug as 

 before. 



7. Before laying the platinum loop on the bench, heat it to redness to 

 destroy any organisms which may still be adhering to it (in this particular 

 .case the anthrax bacillus, an organism pathogenic to man). 



8. See that the tubes have been securely plugged. 



Write on the tube which has been sown the nature of the 

 organism and the date when it was sown. 



It is often convenient to cover the wool plug with a small cap. This 

 is readily done by twisting over the top a small strip of paper, which 

 has been rolled round its upper part. The details of the culture can be 

 written on this (fig. 57) : paper caps, however, are liable to be inter- 

 changed, so that it is at least a wise precaution to label the tube as 

 well. The cap has the advantage that it protects the wool from all 

 liability to contamination. 



Notes. It is of the utmost importance that culture- tubes which 

 have to be opened should be held in an oblique, nearly horizontal 

 position so that dust may not fall into them. 



No time should be wasted during the sowing of cultures, in order to 

 minimize the chances of them becoming contaminated. 



Wool plugs must never be laid on the bench. The part of the plug 

 which goes into the tube ought to be prevented from touching any- 

 thing. 



The handle of the platinum needle should never touch the medium. 



FIG. 57. 

 Culture-tube 

 protected 

 with paper 



B. Method of sowing stroke surface cultures. As an example 

 of this, the sowing of a sloped agar tube may be described. 



1. Proceed as under A, substituting a tube of sterile agar for 

 the sterile broth. 



2, 3, 4, 5. As under A. 



6. Remove the plug from the agar tube, place the end of the 



wire on the lowest part of the surface of the agar, and draw it in a straight 

 or zig-zag line over the medium. 



7, 8. As under A. 



Note. In sowing potato the technique is the same as above, but more pressure 

 must be used in drawing the needle over the surface and a medium or stout wire 

 is desirable. 



