512 



BACTERIOLOGY. 



The Sealing and Keeping of Cultures. 



The method of preserving cultures or specimens of 

 blood, etc., in drawn-out bulb tubes has been touched upon 

 (p. 458). In this connection it is desirable to indicate the 

 methods employed in sealing the ordinary culture tubes. 

 Three or four procedures are resorted to. The tubes may 

 be sealed with rubber caps, corks, sealing-wax, or with 

 paraffin. Thin sheets of rubber may also be used. 



In either case, the cotton plug should be cut close to the 

 end of the tube. It should then be drawn out slightly and 

 rolled rapidly in the flame till the cotton is charred a trifle. 

 The cotton is then pushed into the tube to prevent smold- 

 ering. If the tubes are sealed without this precaution, 

 moulds are liable to develop starting from the cotton plug. 



FIG. 73. The keeping pf cultures in black, paper boxes (F. G. N.). 



The corks or rubber caps should be immersed in mer- 

 curic chloride solution (1-1000) and steamed for at least 15 

 minutes. They can then be used for sealing the tubes. 

 The rubber caps, undoubtedly, are the most convenient for 

 this purpose. They are, however, expensive and are likely 

 to deteriorate on keeping. The corks are not only steril- 

 ized by the exposure to steam, but they are also softened. 

 They can now be easily inserted into the tubes, and a per- 

 fectly tight closure can be obtained. When caps or corks 



