Measuring oxygen consumption with an all-electronic multi-range digital respirometer
Oxygen consumption of animals is often measured for studies in physiological ecology. Usually a closed respiration chamber containing a carbon-dioxide-absorbing substance is used. Oxygen consumed by the animal is either compensated by reduction of the vessel volume (Kratochvil 1976) or replaced by electrolysis (Heusner etal. 1965; Rufeger 1968, 1980). Manometers of various kinds are always employed for pressure transmission. All chambers are kept at constant temperature by a thermostatically controlled water bath. The advantage of an electrolytic respirometer is that the quantity of oxygen generated is linearly dependent only on current and independent of air pressure and temperature. The breathing air composition before, during, and after measurement is constant. After equilibration such a system allows direct oxygen consumption measurements at various environmental temperatures without making corrections. In the apparatus described here power supply, time pulse generator, constant current generator, and the processor which controls the operation and calculates the results are joined in a common box. In front of it the counter displays and the switch board with optical and acoustic signals are arranged. A newly designed manometer with adjustable sensitivity and an infra-red sensor drives a digital position discriminator. This amplification of the manometer reading permits a very simple zero adjustment. All the usual types of gas chamber may be used, for instance equipment consisting only of an electrolytic cell, respiration chamber, and compensating chamber (Heusner et al. 1965), as well as extensive additional fittings, with pump-driven air circulation and separate carbon dioxide and humidity absorption vessels (Moyat 1957; Rufeger 1968, 1980). Contact manometers constructed earlier may be connected on a separate input.
A volumetric micro-respirometer with automatic recording equipment
Whenever oxygen consumption measurements have been recorded automatically during long-term experiments the respirometers used have mostly been of the electrolytic type, where the consumed oxygen is replaced by electrolysis and the duration o f current flow is recorded (MacFadyen 1961; Phillipson 1962; Klekowski and Zajdel 1972; Gutman 1983, and many others). Very few measurements have been attempted with respirometers where oxygen consumption is compensated volumetrically (Tuft 1950; Kratochvil 1974). The present paper describes a volumetrically compensated respirometer for micro-measurements; based on those of Scholander (1950) and Scholander et al. (1952) and the automatic setting of Kratochvil (1974) it produces good results. The respirometer described here possesses the following characteristics: easy handling, high accuracy and an ample variability in adjusting for different purposes and animals. All the manometer and connecting channels are drilled out of a solid block of perspex to which the perspex reaction vessel as well as an identical compensation vessel are attached gastight by means of two neoprene 0 rings. Uncoloured kerosene proved to be the best manometric fluid, especially for use with an automatic setting through a light sensor. This light sensor controls the meniscus o f the manometer and via a relay switches the current of the setting motor on and off. When oxygen is consumed by an animal within the respiration chamber the current is turned on
Frequenzänderungen der Aktivitätsperiodik bei Mäusen im Dauerlicht und Dauerdunkel
Zusammenfassung1. Die Tagesperiodik der Aktivität weißer Mäuse, mit normalerweise 24 Std Periodendauer, wird unter den Bedingungen dauernder Belichtung in Abhängigkeit von der Lichtintensität bis zu 26 Std verlängert.2. Bei Übergang von Dauerlicht zu Dauerdunkel wird die Frequenzminderung der Aktivitätsperiodik schlagartig beendet; es tritt wieder die für das Tier charakteristische Eigenfrequenz mit einer Periodendauer von weniger als 24 Std hervor.3. Auch über Monate im Dauerdunkel gehaltene Tiere behalten eine Periodik ungefähr gleichbleibender Frequenz.