~ ~~~~~~~~~~~~~A cytochemical staining method was developed for the demonstration of hydrogenase activity in hydrogenosomes of Trichomonas vaginalis. After fixation in low concentrations of glutaraldehyde under strictly anaerobic conditions and incubation of these cells in the presence of H2 and the tetrazolium compound 2-(2'-benzothiazolyl)-5-styryl-3-(4'-phthalhydrazidyl)-tetrazolium chloride, an electron-dense deposit was produced in the hydrogenosomes. The method was used to demonstrate the hydrogenosomal nature of similar microbodies of the sapropelic ciliates Plagiopyla nasuta and Trimyema compressum.

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The products of anaerobic and micro‐aerobic (0.8% O2) metabolism of the sapropelic ciliate Trimyema compressum strain N were studied. Under anaerobic conditions ethanol was formed in large amounts representing 44% of the total carbon excreted. Acetate, lactate, formate, CO2 and H2 were minor products, while succinate was formed in hardly detectable amounts. Under micro‐aerobic conditions O2 was consumed, CO2 and formate were produced as major end products and no H2, ethanol and succinate were formed.