SUMMARY1. The effects of graded concentrations of caffeine on the Na efflux were investigated. External application of 10 mm caffeine usually caused a biphasic response, viz, a fall, followed by a rise in the Na efflux. 1 and 5 mm caffeine usually caused stimulation. Only the stimulator phase of this response depended on the presence of external Ca2+.2. Internal application of 100 mm~caffeine caused a small rise in the Na efflux, the magnitude of which was independent of external Ca2+ and comparable to that obtained with external application of 1 mm caffeine. This action, however, could be greatly augmented by pre-treating the fibre with x 10-5 M ouabain.3. The rise in Na efflux caused by external application of 10 mmc affeine could be greatly augmented by pre-treating the fibre with 5 x IO--M ouabain. The observed stimulatory response was biphasic, more so in the absence of external Ca2+. Restoration of external Ca2+ following the onset of the second stimulatory phase resulted in further rise of the Na efflux. Measurements of the Na efflux during treatment with graded concentrations of ouabain and 10 mm~caffeine showed that the rate coefficient for Na efflux varied with the ouabain concentration in the range 10-8_10-4 M. Measurements of the ouabain-insensitive Na efflux before and during treatment with 10 mmw caffeine in bathing media containing varying concentrations of Ca, disclosed the existence of two Ca2+_ thresholds, one in the 0-2-5 mm range and the other in the 12-5-15 mm range.4. Comparisons were made between the effects on the Na efflux of * Permanent address: Department of Biological Sciences, University-of Lancaster, Bailrigg, Lancaster LAI 4YQ, England.1-2 2~~E. EDWARD BITTAR AND OTHERS 10 mm caffeine followed by external acidification, and external acidification, followed by 10 mm caffeine. The magnitude of the response of the ouabaininsensitive Na efflux to external acidification before treatment with 10 mm caffeine was greater than that found when external acidification followed external application of the alkaloid. It also was considerably greater than that of the response to external application of 10 mm caffeine before external acidification.5. External application of 10 mm procaine prevented 10 mmw caffeine from stimulating the Na efflux, and from inducing contractures. Internal application of 100 mm-EGTA reduced the response of the Na efflux to 10 mmw caffeine, and also prevented the fibre from contracting. External application of 10-4m diphenylhydantoin reduced the response of the Na efflux to 10 mmw caffeine but failed to prevent the development of contractures.6. Internal application of 0-05 m-cGMP, cAMP or its dibutyryl derivative caused a large rise in the Na efflux. The magnitude of the effects observed in ouabain-poisoned fibres was often greater than that in unpoisoned fibres. Internal application of 2-5 units/ml. phosphodiesterase beforehand failed to reduce the magnitude of the stimulatory response to injected cyclic nucleotides. Injected phosphodiesterase also failed to reduce th...

Many technical approaches have been proposed for ensuring that decisions made by machine learning systems are fair, but few of these proposals have been stress-tested in real-world systems. This paper presents an example of one team's approach to the challenge of applying algorithmic fairness approaches to complex production systems within the context of a large technology company. We discuss how we disentangle normative questions of product and policy design (like, "how should the system trade off between different stakeholders' interests and needs?") from empirical questions of system implementation (like, "is the system achieving the desired tradeoff in practice?"). We also present an approach for answering questions of the latter sort, which allows us to measure how machine learning systems and human labelers are making these tradeoffs across different relevant groups. We hope our experience integrating fairness tools and approaches into large-scale and complex production systems will be useful to other practitioners facing similar challenges, and illuminating to academics and researchers looking to better address the needs of practitioners.

SUMMARY1. The cation composition of single barnacle muscle fibres following damage by axial insertion of a microsyringe has been measured. The Na and Ca contents of these fibres were raised.2. Electronmicroscopic studies of fibres following insertion of a microsyringe indicated that the damage done resulted in tubular obstruction of the T-system.3. Fibres loaded with radiosodium by micro-injection showed that the Na* efflux declined exponentially with time, but that in most fibres the Injections of distilled water deep in the fibre failed to influence the course of the Na* efflux.4. K removal reduced the Na efflux by 47 %. However, a few fibres displayed very little K-dependence.5. When measured in fibres already soaked in a K-free medium for long periods the sodium efflux consisted of a brief rapid phase, followed by a slow phase of Na loss.6. In the presence of 30 mM-K, there was little or no rise in the Na efflux. Raising the external K to 50 or 100 mm caused a marked rise in the Na efflux. Raising the external K to 30 mm in the absence of external Ca2+ led to a rise in the Na efflux. A high K solution always caused shortening of these fibres.7. Internal application of 1 M or 1 mM-CaCl2 often caused a significant rise in the Na efflux.8. Internal application of 2x5 or 5 M saline caused a prompt and large t Permanent address: Institute of Physiology and Medical Biophysics, University of Uppsala, Uppsala, Sweden. E. EDWARD BITTAR AND OTHERS fall in the Na efflux. In the presence of high K saline-loaded fibres failed to contract.9. Internal application of 0-5 M-ATP stimulated the Na efflux. A larger effect was not observed in fibres pre-treated with 2 M-MgCl2. Internal application of 0 5 m-ArP was without effect.10. The results indicate that the barnacle fibre is a suitable preparation for the study of Na fluxes by means of the micro-injection technique. They also indicate that the mechanism regulating the Na efflux is not quite the same as that found in squid axon or frog muscle.

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Measurements of radiosodium efflux were carried out on single fibres from the barnacle Balanus nubilus or B. aquila, using the micro‐injection technique. 10‐4 M ouabain caused an average fall of 68% of the Na efflux, the minimal effective concentration being ca. 10‐7 M. Internal application of 4 × 10‐3 M ouabain was without effect. Abolition of the ouabain‐sensitive component with ouabain, followed by raising the external K concentration to 30 mM, resulted in a marked rise in the residual Na efflux. Stimulation of the ouabain‐insensitive Na efflux was also seen after reducing the external pH, as well as after microinjecting CaCl2 but not MgCl2. Uncoupling of the active transport system by K removal, followed by external application of ouabain, and subsequent acidification of the bathing medium, led to stimulation which was considerably greater than that taking place when the Na efflux was uncoupled by K removal and then stimulated by external acidification.