Fig. 4.  The effect of 21 and 80% oxygen concentration on the rate of neutrophil phagocytosis shown by the proportion of neutrophils contributing to phagocytosis (contain fluorescent bacteria) with given time is represented. Samples were preincubated with lipopolysaccharide for 15 min before the addition of opsonized bacteria at time 0. The statistically significant finding, represented by the P  value, occurred at 2 min and represents a comparison between 21 and 80% oxygen at that interval. K  ^m50 = time for 50% of neutrophils to contribute to phagocytosis.