SUMMARY1. The electrical and mechanical activity have been recorded from the rat ureter in situ.2. The frequency of peristaltic contractions is usually about 25/min, and each peristalsis is preceded by electrical activity which normally travels from the renal end of the ureter towards the vesicular end. The electrical and mechanical activities are closely correlated. 4. The normal electromyogram probably arises in the first 5 mm of the renal end of the ureter, and retrograde activity may arise from a similar region at the vesicular end of the ureter.5. A close arterial injection technique shows that the proximal end of the ureter behaves as if it possessed a-receptors; the distal end behaves as if it had fl-receptors. This conclusion is discussed. PNTRODUCTION Several studies have been made of the functioning of the ureter of various species (Fagge, 1902;Gruber, 1928;Bozler, 1938;Prosser, Smith & Melton, 1955; Kiil, 1957), but few of them have been on the ureter of the rat, and most of them have used the isolated organ. Although much can be learned from such preparations they cannot demonstrate the normal physiology of the organ and, in particular, they are quite unable to throw light on the still unsolved problem of the role of the innervation of the ureter. In this study the electrical and mechanical activities of the rat ureter have been examined in situ, the ureter being undisturbed except for the removal of the peritoneal membrane covering it.

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Urine entering the caeca of birds contains significant amounts of uric acid. The discovery of great numbers of bacteria utilizing uric acid in the caeca has encouraged the discussion about nitrogen recycling in birds. In this work caecal decomposition of uric acid in wild and captive willow ptarmigan has been investigated using radioactively labelled uric acid injected directly into one of the caeca. The appearance of radioactive CO2 in the expired air was taken as an indication of uric acid breakdown. The decomposition occurred at a rate corresponding to a half-life of 26 min (11-36 min). The results are in accordance with the previously reported observations of huge numbers of uric acid utilizing bacteria in the caeca of a variety of birds, and also with the nitrogen recycling theory. However, no conclusion concerning the nitrogen recycling can be drawn.

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