ABSTRACT
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.
In the absence of precise analyses of rabbit blood, figures taken from Karl Schmidt’s analysis of human blood have been used in this calculation.
I am much indebted to Dr R. A. McCance for showing me the details of this method before publication, and for providing me with the necessary reagents.
Hollande and Cordebard (1926) describe an unrecognised add in large amounts in the excreta of the clothes moth (Tinella bitellidla), but, in spite of their assertions to the contrary, it seems very probable that this is uric add ; and if it is reckoned as such, analysis of their figures shows that 86 per cent, of the uric add in the excreta is in the free form.
Quantitative analysis of the blood of Rhodmui has not been attempted, but it is easy to demonstrate the presence of magnesium in a very small drop of it by the titan yellow test.
It may be recalled that Meissner (1868) showed that the ammonia in the urine of birds was all in the soluble fraction, and not in the uratic spheres.
