Fig. 2. Effect of methazolamide on the alkalization of the midgut using the Bromothymol Blue (BTB) assay of pH within living, but isolated, gut tissue. Gut tubes were dissected after pre-loading with BTB and then incubated for 5 h in hemolymph substitute (Clark et al., 1999) in the absence (A) or presence (B) of 10^–6 mol l^–1 methazolamide. The loss of blue coloration in B shows that the internal pH of the gut lumen has dropped below 7.6. Scale bar, 600 µm.