An adult Rhodnius will ingest from two to three times its weight of blood at a single meal, and about three-quarters of the water in this blood is excreted as a clear fluid during the next three or four hours.

This fluid is alkaline (pH 7.8), more or less isotonic with the blood (sp. gr. 1.007; Δ = 0.62-0.68), and serves for the elimination of most of the sodium and potassium chlorides in the meal. It also contains urea, bicarbonate, sulphate and uric acid.

After the first day, the urine gradually becomes acid (pH 6.0-6.5 and much more concentrated, and contains a yellow pigment. Uratic spheres appear and increase in number until the urine is semi-solid. The urine now contains only traces of sodium, potassium, chloride and urea. There are small amounts of calcium, magnesium, phosphate, sulphate, creatine and probably amino acids. There is never any ammonia.

Almost all the nitrogen is excreted as uric acid. This is in the form of minute spheres with radial striation, in which about 80 to 90 per cent, of the uric acid is free; the rest, presumably, as sodium and potassium acid urate.

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