460 



CONTROL OF CULTURES 



This method, employing the use of semisohd media, appears to be 

 appHcable for many types of Protozoa. The consistency of the medium 

 through which the Protozoa migrate seems to favor the removal of bac- 

 teria, in that vigorous motion is necessary. The bacteria, on the other 

 hand, would be largely prevented from dispersing far from the point 

 of inoculation, at least for some time. This method, or some modification 

 of it, should receive serious consideration from future investigators, in- 



Figure 125. V migration 

 tube for semisolid media. 

 The Protozoa to be steril- 

 ized are injected through 

 the small arm and deposited 

 at the bottom of the V.They 

 migrate up through the 

 semisolid medium and are 

 removed at the top of the 

 large arm. (Redrawn from 

 Glaser and Coria, 1930.) 



terested in the problems arising from the use of bacteriologically sterile 

 protozoa. 



C. Combinations of dilution and migration. — Cleveland (1928) de- 

 scribed in detail the various manipulations which he employed to effect 

 the sterilization of Tritrichomonas jecalis, a flagellate parasitic in the hu- 

 man intestine. The method which yielded consistently satisfactory results 

 was a combination of washing and migration. The flagellates to be steril- 

 ized were concentrated by centrifugation, and the supernatant fluid drawn 

 off with sterile pipettes. The packed flagellates were than layered onto 

 the surface of sterile fluid (serum-saline) in centrifuge tubes, and the 

 centrifuging process repeated. This procedure was continued through 

 twenty sets of tubes, at which time Cleveland states that the ratio of 

 Tritrichomonas to bacteria was about fiftv to one. This constituted the 



