Mass transfer to fluids flowing through rotating nonaligned straight tubes

Relatively inefficient heat/mass transfer is characteristic of tubular devices if the Reynolds number is low. One method of improving the heat/mass transfer efficiency of such devices is by inducing transverse laminar secondary circulations that are superimposed on the primary flow field; the resulting transverse velocity components lead to fluid mixing and hence augmented mass transfer in the tube lumen. The present work is a theoretical and experimental investigation of the enhanced transport in rotating, nonaligned, straight tubes, a method of transport enhancement that utilizes Coriolis acceleration to create transverse fluid mixing. This technique couples the transport advantages of coiled tubes with the design advantages of straight tubes. The overall mass balance equation is numerically solved for transfer into fluids flowing steadily through rotating nonaligned straight tubes. This solution, for small Coriolis disturbances, incorporates a third order perturbation solution for the primary and secondary flow fields. For sufficiently small Coriolis disturbances the bulk concentration increase is found to be uniquely determined by the value of a single similarity parameter. As the Coriolis disturbance is increased, however, two additional parameters are required to accurately characterize the mass transfer. In general, increasing the Coriolis accelerations results in an increase in mass transfer. There are solution regimens, however, in which increasing this acceleration can lead to a decrease in mass transfer efficiency. This interesting phenomena, which has important design implications, appears to result from velocity-weighting effects on the exiting sample. Experiments, involving the measurement of oxygen transferred into water and blood, produced data that agree with the theoretical predictions.     

Mixing time and oxygen transfer characteristics of double draft tube airlift fermentor

Despite the increasing importance of airlift fermentors, very little published information is available on how the geometric configurations of the draft tubes and the air-sparging system affect the mixing and oxygen transfer characteristics of the fermentor. A 14-L air-lift fermentor was designed and build with a fixed liquid height to diameter ratio of 1.5 utilizing four equally spaced air jets at the bottom. Two jet orifice sizes were used, 1.27 and 3.81 mm i.d., and for each jet size the following four geometric configurations were used: Single inner concentric draft tube, single outer concentric draft tube, two concentric draft tubes, and no draft tubes where the fermentor was operated as a shallow bubble column. It was found that the presence of draft tubes stabilized liquid circulation patterns and gave systemically higher mixing times than those obtained in the absence of draft tubes. In addition, the double draft tube geometry resulted in higher mixing times than the single draft tubes. For the power unit volume range 20 to about 250 W/m³ the larger 3.81-mm orifices gave systemically higher k_L a values than the smaller 1.27-mm i.d. orifices. At 200 W/m³ the use of a single outer draft tube with the 3.81-mm orifices resulted in 94% increase in k_L a values over that obtained with no draft tubes. However, the effect of draft tube geometry on k_L a values when the 1.27-mm orifices were used was not significant. The air bubble formation characteristics at the jet orifices were found to be different, which reflected the differences observed in mass transfer and mixing characteristics. The power economy for oxygen transfer was found to be depend strongly on the orifice size and less on the geometric configuration of draft tubes.     

Transport processes during sterilization of vertical and 5 degree horizontal dead-legs

Experimental temperature profiles and biological kill data from dead-ended tubes of various diameters and lengths commonly used in biotechnology applications were compared to those predicted by a finite element model for steam-in-place (SIP) sterilization at 122°C. Diameter was shown experimentally and numerically to have a significant effect with larger diameter tubes exhibiting greater buoyant driven convective flow and more rapid sterilization. The overall Grashof number was shown to be the significant parameter relating magnitude of convective flow to tube diameter and varied as the diameter cubed. Analysis of air/steam mixture flow patterns showed air displacement from 0.4 cm diameter tubes to be due primarily to molecular diffusion, whereas 1.0 and 1.7 cm tubes showed a two-stage convective flow pattern. There exists a critical diameter of 0.4 cm below which SIP sterilization due to buoyancy driven flow does not occur and steam bleeders should be used.     

Regulation of exoprotease production by temperature and oxygen in Vibrio alginolyticus

The production of an extracellular collagenase and an alkaline protease by Vibrio alginolyticus during stationary phase was inhibited by a temperature shift from 30 to 37°C and by a lack of oxygen. The stability of the exoproteases was unaffected by incubation at 37°C and aeration. The optimum growth temperature for the V. alginolyticus strain was 33.5°C Aeration enhanced the rate of growth of exponential phase cells. Temperature and oxygen did not affect the growth of stationary phase cells when the exoproteases were being produced. Macromolecular synthesis in stationary phase cells was not affected by temperature. There was no rapid release of the exoproteases after temperature shift down and chloramphenicol inhibited the production of the enzymes when added at time of temperature shift down from 37 to 30°C. The regulation of exoprotease production by temperature and oxygen was specific and has implications regarding the ecology of V. alginolyticus. Cerulenin, quinacrine and O-phenanthroline inhibited the production of the exoproteases.     

Factors affecting spore germination in Aspergillus niger

Temperature markedly affected germination and germ tube length of A. niger. More than 90% of the spores were germinated in the range 30°–34 °C and formed maximum length of germ tubes. At temperatures from 38° to 43 °C, the proportion of the spores that germinated as well as the germ tube length were both gradually decreased. However, at 47°C germ tube formation was completely inhibited up to 15 hrs. after inoculation.High relative humidity was found necessary for the spore germination of A. niger. Germination failed to occur at 76% relative humidity. At 78 and 81% relative humidity germination was detected 15 hrs. after inoculation while at the higher humidities germination was started after 6 hrs. only.Conidiospores of A. niger were very sensitive to changes in the hydrogen ion concentration, pH. Complete inhibition of germination was found at pH less than 3.5. The germination and the length of the formed germ tubes increased with pH to reach their maximum rates at pH 4.5.     

Respiratory quotient and ammonia quotient in Tilapia mossambica (Peters) with special reference to hypoxia and recovery

At oxygen concentrations below air saturation, R.Q. and A.Q. values of Tilapia mossambica increase with decrease in ambient oxygen at 30 and 35°C, indicating an increase in anaerobic metabolism and protein utilization. The recovery metabolism indicates that T. mossambica accumulates an oxygen debt at 30°C, which was not obvious at 35°C. The post-hypoxic oxygen consumption at 30°C is quite pronounced and the fish repays almost wholly the oxygen debt accumulated. At 30°C, R.Q. and A.Q. reach prehypoxic level immediately after exposure to high oxygenated water. In contrast to this, during recovery the first high R.Q. which is higher than unity and subsequent low R.Qs., almost as low as 0.5, suggest respectively that, anaerobic energy utilization persists and carbon dioxide is retained. The differences in the recovery metabolism of T. mossambica at the two temperatures may be due to changes in metabolism and pathways due to temperature. The recovery metabolism of T. mossambica suggests that energy derived anaerobically could proceed through other pathways than the conventional glycolytic way. The decrease in random activity during the hypoxic phase at 30 and 35°C may have a special significance for survival.From a thesis (M.P.M.) approved for the degree of Doctor of Philosophy, Madurai University, Madurai, India.From a thesis (M.P.M.) approved for the degree of Doctor of Philosophy, Madurai University, Madurai, India.     

Photosynthetic efficiency of Chlorella sorokiniana in a turbulently mixed short light‐path photobioreactor

To be able to study the effect of mixing as well as any other parameter on productivity of algal cultures, we designed a lab‐scale photobioreactor in which a short light path (SLP) of (12 mm) is combined with controlled mixing and aeration. Mixing is provided by rotating an inner tube in the cylindrical cultivation vessel creating Taylor vortex flow and as such mixing can be uncoupled from aeration. Gas exchange is monitored on‐line to gain insight in growth and productivity. The maximal productivity, hence photosynthetic efficiency, of Chlorella sorokiniana cultures at high light intensities (1,500 μmol m^?1 s^?1) was investigated in this Taylor vortex flow SLP photobioreactor. We performed duplicate batch experiments at three different mixing rates: 70, 110, and 140 rpm, all in the turbulent Taylor vortex flow regime. For the mixing rate of 140 rpm, we calculated a quantum requirement for oxygen evolution of 21.2 mol PAR photons per mol O₂ and a yield of biomass on light energy of 0.8 g biomass per mol PAR photons. The maximal photosynthetic efficiency was found at relatively low biomass densities (2.3 g L^?1) at which light was just attenuated before reaching the rear of the culture. When increasing the mixing rate twofold, we only found a small increase in productivity. On the basis of these results, we conclude that the maximal productivity and photosynthetic efficiency for C. sorokiniana can be found at that biomass concentration where no significant dark zone can develop and that the influence of mixing‐induced light/dark fluctuations is marginal. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Utilizing the tubular bioreactor for continuous recovery of secreted fusion protein from recombinant Escherichia coli

In order to improve the cultivation properties of a traditional continuous stirred tank reactor (CSTR), we introduced a circulation unit made of four inorganic membranes in stainless steel tubes in parallel configuration, the so-called Tubular Bioreactor (TBR). Furthermore, the TBR outlet tube, which has a restriction nozzle at the end, was installed on top of the fermentor vessel, thereby creating a strong jet flow into the reactor and thus improving the mixing and the oxygen transfer rate. The k _La could be increased by approximately 50%. This setup was used for cultivations of recombinant Escherichia coli in a minimal medium and high cell density. More than 50 g dry cell mass/dm³ was obtained. Simultaneously, we have produced an elongated form of human insulin-like growth factor II, which was a secreted fusion protein utilizing the E. coli secretion system based on staphylococcus protein A. The product could be recovered continuously through the TBR-membrane.     

Soil temperature effects from minirhizotron lighting systems

Observing root dynamics or soil fauna with minirhizotrons requires the use of incandescent or ultraviolet (UV) lighting systems. These light sources can generate heat which would be transferred to the surrounding soil adjacent to the minirhizotron observation tubes and thus may influence root growth and development or fauna activity. The objective of this study was to determine the effect of incandescent and UV light from a minirhizotron camera system on soil temperatures next to minirhizotron tubes. Temperature probes were attached next to and at 0.5 cm from the tube surface and the tubes were then placed in boxes with either a fine sand or a loamy clay soil. Incandescent light was operated stationary for 5 min or moved at 1 cm increments every 10 s down the tube for both dry and wet soils. The UV light was used in a stationary position for 10 minutes in both dry soils. Maximum temperature increases were 3.41–3.52 °C and 1.69–2.14 °C next to the tube for the dry and wet soils, respectively with 5 min of stationary incandescent light. Ultraviolet lights increased soil temperatures to a maximum of approximately 2.5 °C in the dry soil. Probes placed 0.5 cm from the tube surface also showed temperature increases up to 2.15 °C. Moving the light source every 10 s, however, resulted in lower temperature increases (<0.8 °C). Therefore short durations of light resulted in small temperature increases suggesting minimal impact on root development. Increased soil temperatures from longer durations of light, however, may alter root growth and development as well as soil fauna activity and warrants further study.     

Physiological studies on Biomphalaria alexandrina and Bulinus truncatus,the snail vectors of Schistosommiasis

Summary The Warburg's manometric technique was used to measure the rate of oxygen consumption of the second generation of laboratory-reared snails, Biomphalaria alexandrina and Bulinus truncatus at two temperatures of 25° and 30°C. The individual weight of the experimental snails ranged between 40 and 78 mg for B. alexandrina, between 60 and 90 mg for B. truncatus.At 25°C, the uninfected snails B. alexandrina consumed oxygen at an average rate of 0.096 ± 0.020 ml/g wet wt/hr. The rate of oxygen consumption increased to an average of 0.147 ± 0.008 ml/g wet wt/hr for uninfected snails maintained at 30°C (about 53 per cent increase). The average RW value for uninfected snails maintained at 25°C was 0.80.The snail Bulinus truncatus showed higher oxygen requirements than the snail Biomphalaria alexandrina. At 25°C, it consumed oxygen at an average rate of 0.124 ± 0.016 ml/g wet wt/hr. At 30°C, the rate of oxygen consumption reached a value of 0.220 + 0.006 ml/g wet wt/hr. The average RQ for Bulinus truncatus maintained at 25°C was 0.87.The rate of oxygen consumption of the schistosome — infected Biomphalaria alexandrina snails, maintained at 25°C decreased to an average rate of 0.059 ± 0.010 ml/g wet wt/hr, (an average of 39 per cent decrease). The respiratory quotient (RQ) also decreased to an average value of 0.58. Further research is suggested to clarify the metabolism of both schistosome-infected and uninfected snails.Read at the Ist African Symposium on Bilharziasis, Cairo Egypt, U.A.R., February, 1969.From the Laboratory of Bilharziasis Research, National Research Centre, Dokki, Egypt, U.A.R.     

Influence of temperature on the optimal hematocrit of the bullfrog (Rana catesbeiana)

Summary The influence of temperature on blood viscosity and consequently on the potential for oxygen transport by blood was determined using a controlled flow, variable pressure tube viscometer, and blood from adult bullfrogs. Blood viscosity was determined as a function of hematocrit and temperature, and oxygen capacity was determined as a function of hematocrit. These data were used to describe 1) the potential for oxygen transport in the tube viscometer, and 2) the relation between the optimal hematocrit, the hematocrit which provided the greates oxygen transport, and temperature. The optimal hematocrit increased at a rate of 0.237% per °C increase in temperature. This value is close to the rate of change inin vivo hematocrit of 0.246 and 0.240% per °C increase in body temperature (T_b) observed in winter bullforgs acclimated to 5 and 20°C, respectively. During the summer the hematocrit ratio showed no consistent relation to T_b. These results suggest that in bullfrogs the cardiovascular adjustments to change in T_b involve the optimal hematocrit in winter, but not in summer.     

Daily rhythm of oxygen consumption and thermoregulatory responses in some European winter- or summer-acclimatized finches at different ambient temperatures

The oxygen consumption of European finches, the siskin (Carduelis spinus), the brambling (Fringilla montifringilla), the bullfinch (Pyrhulla pyrhulla), the greenfinch (Carduelis chloris) and the hawfinch (Coccothraustes coccothraustes), was recorded continuously while ambient temperature was decreased stepwise from +30 down to-75°C. The oxygen consumption, body temperature (telemetrically), and shivering (integrated pectoral electromyography) of greenfinches were measured simultaneously at ambient temperatures between +30 and-75°C. Maximum heat production, cold limit, lower critical temperature, basal metabolic rate and thermal conductance (of the greenfinch) were determined. The diurnal variation of oxygen consumption of siskins and greenfinches was recorded at thermoneutrality and below the thermoneutral zone in winter- and summer-acclimatized birds. The diurnal variation of body temperature and thermal conductance of greenfinches were also determined. The diurnal variation of heat production was not seasonal or temperature dependent in the siskin and in the greenfinch. Nocturnal reduction of oxygen consumption saved 15–33% energy in the siskin and greenfinch. Body temperature of the greenfinch was lowered by 2.5–3.4°C. The nocturnal reduction of thermal conductance in the greenfinch was 39–48%. The basal metabolic rate was lowest in the largest bird (hawfinch) and highest in the smallest bird (siskin). The values were in the expected range. The heat production capacity of finches in winter was 4.7 times basal metabolic rate in the siskin, 4.2 times in the brambling, 3.5 times in the greenfinch and 2.9 times in the bullfinch and hawfinch. The heat production capacity of the siskin and greenfinch was not significantly lower in summer. The cold limit temperatures (°C) in winter were-61.2 in the siskin,-41.3 in the greenfinch,-37.0 in the bullfinch,-35.7 in the brambling and-28.9 in the hawfinch. The cold limit was 14.3°C higher in summer than in winter in the siskin and 8.7°C in the greenfinch. Thermal insulation of the greenfinch was significantly better in winter than in summer. The shivering of the greenfinch increased linearly when ambient temperature was decreased down to-40°C. Maintenance of shivering was coincident with season. In severe cold integrated pectoral electromyography did not correlate with oxygen consumption as expected. The possible existence of non-shivering thermogenesis in birds is discussed. It is concluded that the acclimatization of European finches is primarily metabolic and only secondly affected by insulation.Abbreviations AAT avian adipose tissue - bm body mass - BMR basal metabolic rate - C _t thermal conductance - EMG electromyogram - HP heat production - HP _max maximum heat production - MR metabolic rate - NST non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a ambient temperature - T _b body temperature - T _c colonic temperature - T _1c lower critical temperature - TNZ thermoneutral zone - T _st shivering threshold temperature - V oxygen consumption     

Respiratory,cardiovascular and metabolic adjustments during steady state swimming in the green turtle,Chelonia mydas

Summary Heart rate and pulmonary artery blood flow of resting green turtles,Chelonia mydas, at 29°C increased with lung ventilation (heart rate from 24±5 to 51±8 beats min). When swimming at 0.6 m s^–1 in water at 30°C, oxygen uptake was 2.83 times and respiratory frequency was 2.75 times the resting values. Heart rate was 1.33 times that during ventilation at rest but 2.83 times that at the end of a breath hold at rest. Partial pressures of oxygen and carbon dioxide, lactic acid concentration and pH of arterial blood, when swimming at 0.5 m s^–1, were similar to those soon after ventilation at rest. Pulmonary blood flow did not decline to low levels between breaths, when the animals were swimming, as it did when they were at rest.In active turtles it appears that pulmonary perfusion remains elevated, supplying oxygen to the locomotory muscles at a sufficiently high rate to support the complete aerobic production of energy, and that respiratory frequency is kept as low as possible, as surfacing for air increases the metabolic cost of swimming.     

Pressure change and gas mixing induced by oscillations in a closed system

In an attempt to delineate some mechanical behaviors found in branching airways, pressure transmission, gas motion, and mixing were studied during high-frequency oscillation (HFO) in an idealized system consisting of a large straight tube and a rigid sphere linked together by a small straight tube. Depending on the frequency f, and on the unsteadiness dimensionless parameter alpha, pressure amplitude in the large tube is either strongly attenuated or amplified in the sphere. This finding may provide a theoretical basis for the pressure resonance phenomenon observed in the lung by previous investigators. Gas compression in the closed volume causes convective mixing throughout the system. The measured dispersion was found to be proportional to f(VT/A)2, in agreement with a recent report. However, bulk convective mixing was sufficient to explain the dispersion for oscillatory volumes (VT) as small as 80 percent of the small tube volume, as has been previously suggested.     

Effects of storage at low-temperature of various heteropteran host eggs on the egg parasitoid, <Emphasis Type="Italic">Trissolcus semistriatus</Emphasis>

Various heteropteran host eggs stored under two low-temperatures were tested in the laboratory for their usability in the production of sunn pest egg parasitoid, Trissolcus semistriatus. Parasitism, adult emergence rate and development time were assesed on stored and fresh eggs of Eurygaster integriceps, Dolycoris baccarum, Graphosoma lineatum and Eurydema ornatum. Masses of fresh host eggs in microcentrifuge tubes were maintained at +6 °C and −20 °C. Every 30 days, 50 eggs of host species were exposed to parasitism by T. semistriatus. The host eggs stored at 6 °C remained viable to parasitism by T. semistriatus up to 2 months, while those of stored at −20 °C were parasitized at high rates up to 4 months, alhough succesful parasitism rates decrease with time. However, it was indicated that both fresh or stored E. ornatum eggs were not preferred to parasitism by the parasitoid. A longer development time from egg to adult was observed in stored eggs under two tested storage techniques when compared with fresh eggs.     

Oxygen effect on batch cultures of Leuconostoc mesenteroides: relationship between oxygen uptake,growth and end-products

Growth and lactose metabolism of a Leuconostoc mesenteroides strain were studied in batch cultures at pH 6.5 and 30° C in 101 modified MRS medium sparged with different gases: nitrogen, air and pure oxygen. In all cases, growth occurred, but in aerobiosis there was oxygen consumption, leading to an improvement of growth yield Y _x/s and specific growth rate compared to anaerobiosis. Whatever the extent of aerobic growth, oxygen uptake and biomass production increased with the oxygen transfer rate so that the oxygen growth yield, Y _x/o2, remained at a constant value of 11 g dry weight of biomass/mol oxygen consumed. Pure oxygen had a positive effect on Leuconostoc growth. Oxygen transfer was limiting under air, but pure oxygen provided bacteria with sufficient dissolved oxygen and leuconostocs were able to consume large amounts of oxygen. Acetate production increased progressively with oxygen consumption so that the total molar concentration of acetate plus ethanol remained constant. Maximal Y _x/s was obtained with a 120 l/h flow rate of pure oxygen: the switch from ethanol to acetate was almost complete. In this case, a 46.8 g/mol Y _x/s and a 0.69 h^–1 maximal growth rate could be reached.     

Comparative growth of the thermal alga Cyanidium caldarium on nitrate and ammonia at different temperatures

Summary The growth of Cyanidium caldarium on nitrate and ammonia as nitrogen sources was studied at different temperatures from 21 to 54°C.Algal growth occurred at temperatures of 24° C or above when ammonia was the nitrogen source, whereas with nitrate, growth occurred at 30° C or above. The optimum and the maximum growth temperatures were 45 and 54° C respectively on both substrates.Arrhenius plots show that the logarithm of the growth rate is not linear with the reciprocal of absolute temperature, but exhibit sharply defined breaks at 30° C on ammonia and at 40° C on nitrate.It is assumed that below 40° C, when Cyanidium grows on nitrate, the utilization of this substrate represents the master reaction which controls the growth rate of the alga.     

Production of extracellular inulinase in high-cell-density fed-batch cultures of Kluyveromyces marxianus

The production of extracellular inulinase (\-1,2-d-fructan fructanohydrolase, EC 3.2.1.7) was studied in fed-batch cultures of the yeast Kluyveromyces marxianus CBS 6556 at 30 and at 40° C. At both temperatures, the final biomass concentration exceeded 100 g·l^–1 and more than 2 g enzyme. L^–1 of culture supernatant was produced. The biomass yield on O₂ at 40° C was substantially lower than at 30°C. Nevertheless, at 40° C a growth rate of 0.20 h^–1 could be maintained for a longer period than at 30° C. The unexpected higher O₂-transfer rate at 40°C is probably due to a lower viscosity of the culture broth. The 40°C fermentation took only 33 h as compared to 42 h at 30° C. These results indicate that K. marxianus is a promising host for the extracellular production of heterologous proteins under the control of the inulinase promoter.     

Bolus contaminant dispersion in oscillating flow in curved tubes.

The investigation of longitudinal dispersion of tracer substances in unsteady flows has biomechanical application in the study of heat and mass transport within the bronchial airways during normal, abnormal, and artificial pulmonary ventilation. To model the effects of airway curvature on intrapulmonary gas transport, we have measured local gas dispersion in axially uniform helical tubes of slight pitch during volume-cycled oscillatory flow. Following a small argon bolus injection into the flow field, the time-averaged effective diffusion coefficient (Deff/Dmol) for axial transport of the contaminant was evaluated from the time-dependent local argon concentration measured with a mass spectrometer. The value of (Deff/Dmol) is extracted from the curve of concentration versus time by two techniques yielding identical results. Experiments were conducted in two helical coiled tubes (delta = 0.031, lambda = 0.022 or delta = 0.085, lambda = 0.060) over a range of 2 < alpha < 15, 3 < A < 15, where delta is the ratio of tube radius to radius of curvature, lambda is the ratio of pitch height to radius of curvature, alpha is the Womersley parameter or dimensionless frequency, and A is the stroke amplitude or dimensionless tidal volume. Experimental results show that, when compared to transport in straight tubes, the effective diffusivity markedly increases in the presence of axial curvature. Results also compare favorably to mathematical predictions of bolus dispersion in a curved tube over the ranges of frequency and tidal volume studied.     

Physiological significance of behavioral hypothermia in hypoglycemic frogs (Rana catesbeiana)

Hypoxia elicits a number of compensatory responses in animals, including behavioral hypothermia. The hypothesis that hypoglycemia induces hypothermia in the bullfrog Rana catesbeiana was tested and that this behavioral response would be beneficial. Frogs equipped with a temperature probe were tested in a thermal gradient (10–40°C). Insulin (15 IU kg⁻¹) caused significant reduction of body temperature, from 25.0 to 17.8°C. A non-metabolizable glucose analogue, 2-deoxy-d-glucose (2-DG, 50 mg kg⁻¹),which blocks intracellular glucose utilization, was also injected and caused a similar drop in body temperature, despite an increase in plasma glucose levels. To assess the possible benefits of hypoglycemia-induced hypothermia, the effects of insulin and 2-DG injections were measured on plasma glucose concentration and on oxygen consumption of frogs equilibrated at 10, 20 and 30°C. The plasma glucose was elevated at higher temperatures and so was oxygen consumption. The insulin caused a significant reduction of plasma glucose concentration (about 1.22 μMol ml⁻¹) whereas 2-DG caused a significant increase (about 0.70 μMol ml⁻¹) at 30°C. Both drugs caused a reduction of oxygen consumption (approximately 0.388 and 0.382 ml min⁻¹ kg at 30°C after insulin and 2-DG injection, respectively). No effect of either insulin or 2-DG was observed when the animals were equilibrated at 10°C. In conclusion, hypothermia may be a beneficial response to hypoglycemia in frogs.