456 



CONTROL OF CULTURES 



hominls. Their capillary tube was made from a piece of 6 mm. Pyrex 

 tubing about eight inches in length, which, before sterilization, had been 

 plugged at both ends with cotton. The capillary was then drawn from one 

 end of the tube, its tip broken off with sterile forceps, and a series of 



Lq 



Figure 123. Capillary 

 tube used for the steriliza- 

 tion of TricJjOfnonas ho- 

 minis. The whole tube is 

 filled with sterile fluid, the 

 lower end sealed in a flame, 

 and the Protozoa to be ster- 

 ilized are layered on to the 

 fluid at the large end. The 

 Protozoa eventually migrate 

 through the capillary por- 

 tion, but the associated bac- 

 teria are trapped at the first 

 or second bend. (Redrawn 

 from Stone and Reynolds, 

 1939.) 



loops constructed (Fig. 123). All of these manipulations were carried 

 on with care not to contaminate the outside of the tube, for after the 

 loops were made the whole tube was filled to within one inch of the top 

 with sterile fluid (in this case, one part Ringer's, eight parts horse serum) 

 by suction, applied to the large end. The capillary end was then sealed 

 off and the tube, in a vertical position, was incubated forty-eight hours 



