PASTEUR'S TUBES 



95 



exhausted as before, and the inlet-tube sealed off at the lower 

 constriction. 



The above method is equally applicable to cultures upon agar, 

 gelatine, and other media, provided that the usual precautions are 

 taken to first get rid of the oxygen in suspension or solution. 



12. 



Pasteup's tubes— 



These tubes, three forms of which are shown on figure, are at 

 times useful for cultivations in liquid media. Form "A" is of 

 special service in studying the phenomena attendant upon the 

 " association " of organisms. A constriction is made in the upright 



Fig. 29. — Pasteur's tubes for cultivation of anaerobes. 



tube at the point " c" a light cotton-wool plug inserted above it, 

 and the orifice of the tube is then slightly closed by turning the 

 end in the Bunsen flame (or making a second constriction above 

 the cotton-wool plug) in order to prevent the escape of the cotton- 

 wool on a vacuum being formed. The extreme points of the 

 lateral tubes are sealed in the flame, and the whole is then sterilised 

 at 1 50^ in the hot-air steriliser. 



When required for use, snip off one of the lateral points, pass 

 the pipette portion of the tube through the flame, plunge it into a 

 tube of liquid medium inoculated with a trace of one of the 

 organisms it is desired to study, and aspirate the contents into the 

 tube "a." Seal off the point in the flame, snip off the point of 



