Volume s1-24, Issue 3
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



A comparison of the cysticidal and bactericidal effects of chlorine and ozone is made at pH levels ranging from 5 to 9 in which the test solutions were buffered to hold at constant levels for the duration of the experiment. Cysts of and the bacteria occurring in the routine cultures of the same were tested. One hundred cysts per cc. were selected as a standard dosage for the experiments, the bacterial count accompanying this dosage ranging between 500,000 and 1,000,000 per cc. Chlorine residuals of 0.5 p.p.m. and 1.0 p.p.m. were compared with an ozone residual of 0.3 p.p.m. at time intervals ranging from 2 minutes to 240 minutes at a temperature of 27°C. The following generalizations may be made:

  • 1.  Gaseous chlorine producing a residual of 0.5 p.p.m. when compared with H. T. H. producing the same residual was in general more active.
  • 2.  The activity of chlorine tended to decrease at the higher pH levels studied, while the activity of ozone was less at pH 6 than at pH 5, but was not reduced between pH 6 and pH 9.
  • 3.  No great differences were noted between the bactericidal and cysticidal effects of the loads tested. It must be noted that the bacterial load tested was unusually heavy, and if a bacterial load of 100 to 1000 per cc. were tested the bactericidal times would have been lower.
  • 4.  The bactericidal and cysticidal times required by ozone producing a residual of 0.3 p.p.m. were several times less than those required by chlorine producing residuals of either 0.5 p.p.m. or 1.0 p.p.m.
  • 5.  A buffered liver infusion agar base with a buffered serum mixture is described as an encystment medium for . The results of cyst production on this medium are compared with cyst production on Boeck-Drbohlav's Ringer's-Egg-Serum, Cleveland-Collier's Difco-Entamoeba Medium (2% agar), Locke's Solution and Rice Starch, and Chang's Buffered Liver-Infusion Broth. In our hands the buffered liver infusion agar was superior in cyst production to the other media tested.


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  • Received : 08 Dec 1943
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