Application of the murexide test to Amoeba verrucosa and Paramecium caudatum

Observations made on the distended contractile vacuoles of Amoeba verrucosa subsequent to the application of the murexide test give no optical evidence of the presence of uric acid in the vacuolar fluid. This result is not in accord with the generally accepted conclusions of Griffiths 1 who reported the production of “prismatic crystals of murexide” on application of this test to Amoeba proteus, Vorticella and Paramecium. Mass cultures of Amoeba verrucosa, killed in 50 per cent. alcohol, show the contractile vacuoles fixed at partial or complete expansion in a large percentage of cases, but a critical examination of the fluid of the vacuoles has never revealed the presence of uric acid crystals precipitated there by this method. Dark field examination of such animals shows the fluid to be structureless. Treatment with nitric acid and ammonia in the manner described by Griffiths colors both cytoplasm and pellicle a lemon yellow. Furthermore, control slides, consisting of a small quantity of pure uric acid crystals in distilled water, when similarly treated, also give a negative result. Such controls give ammonium purpurate only on being evaporated to complete dryness, a procedure obviously so drastic as to render it inapplicable in the case of protozoan cells where it is essential to preserve the vacuole and its contents intact. Mass cultures so treated leave a lemon yellow residue.

Cultures of Paramecium, concentrated by brief centrifuging, and subjected to the same test also offer only negative results. Examination of the vacuolar fluid is precluded in these forms by the contraction of the vacuoles during the process of fixation.

This would indicate, therefore, either that uric acid is not an end product of the katabolic activity of these protozoa, or that the murexide test is not sufficiently sensitive to give a satisfactory optical reaction in this case. In view of the latter possibility, other and more specific methods for determining the presence of uric acid in minute quantities, are being applied at the present time.