The hippocampus and septal area as primary target sites for corticosterone

—Two groups of totally adrenalectomized male rats (220-260 g) were injected intraperitoneally with different amounts of [1,2-³H] corticosterone. One group received 1 μg of hormone (50 μCi/μg), and the other received 20 μg (2·5 μCiμg). All animals were decapitated at 15 min and various tissues including the pituitary, cerebellum, pons-medulla, cerebral cortex, hypothalamus, septal area, and hippocampus were assayed for radioactivity and protein content. In the 1-μg group, the hippocampus contained more cpm/mg of protein (P<0·05) than all the other areas including the hypothalamus. The septal area and pituitary gland values were higher (P<0·05) than all the other areas except the hippocampus. In the 20-μg group there was a significant reduction (P<0·05) in the values (cpm/mg of protein) for the hippocampus, septal area and cerebral cortex, but no change in the values for the pituitary, hypothalamus, and pons-medulla. These data suggest that the hippocampus and septal area are primary target sites for corticosterone because they take up more hormone than other nervous tissue loci and demonstrate a limited capacity for hormonal uptake. The pituitary gland tends to concentrate the hormone but does not demonstrate a limited capacity for uptake. The hypothalamus does not concentrate the hormone or demonstrate a limited capacity for uptake, and the data suggest that it is not a primary target site for corticosterone.     

Kinetics of microtubule formation after cold disaggregation of the mitotic apparatus

The rate of spindle-fiber reformation following cold treatment of the giant amoeba, Chaos carolinensis, has been determined and used to test a single growth point, subunit incorporation model of microtubule assembly. Mitotic apparatuses isolated at one-minute intervals after rewarming contain progressively longer spindle fibers; re-assembly begins at the kinetochore region, proceeds at a rate of 1·5 μm per minute, then slows as the normal length of 5 μm is approached. From information on microtubule ultrastructure, the total number of 40-Å subunits in mitotic apparatuses per amoeba, and hence the concentration released during disassembly, was calculated to be 1·0 × 10¹⁵ molecules per cm³. Calculation of diffusion and assembly kinetics indicates that this concentration of microtubule subunits is equal to the concentration required to produce a growth rate of 1·5 μm per minute by diffusion of single subunits to one assembly point per microtubule.     

Dietary cholesterol requirements of housefly, Musca domestica, larvae.

Quantitative analyses have been made of the dietary cholesterol requirement for the growth of the larvae of Musca domestica. The larvae will not grow on diets to which no cholesterol is added, a few pupae and adults are obtained when the concentration of cholesterol is 0·05 μmol/g of diet, but the concentration has to be raised to 0·36 μmol/g of diet before the maximum numbers of pupae and adults are obtained. Further addition of cholesterol above 0·36 μmol/g diet did not have any significant effect on the weight and growth of the larvae. However, the ratios of the cholesterol to phospholipid fractions recovered from the larvae increased rapidly when the concentration of cholesterol in the diet was raised from 0·05 to 0·56 μmol/g of diet. Above this concentration only a slight increase in the ratios was observed. Larvae reared on diets containing 0·05 μmol cholesterol/g of diet contain only 25 per cent of the cholesterol content of the larvae reared on the diets containing more than 0·28 μmol of cholesterol/g of diet, the cholesterol content being expressed relative to the weight of the larvae,The absence of cholesterol synthesis has been demonstrated in the larvae by feeding [4-¹⁴C] cholesterol. The specific activity of the cholesterol recovered from the larvae is the same as that of cholesterol added to the diet. Irrespective of the cholesterol concentration of the larval diet, approximately 97 per cent of the radioactivity recovered from the larvae behaved as free cholesterol, less than 1 per cent as cholesterol esters and the rest as unidentified ‘polar sterols’. The results are compared with those from similar studies on other insects.     

Size and number of nerve fibres in the central nervous system connectives of the cockroach Blaberus craniifer

The size and number of axons in the ventral cord connectives of the cockroach Blaberus craniifer were determined from montages constructed of electron micrographs of the left connective of each of the connective pairs examined. The fibres were grouped into three main diameter categories: fine fibres from 0·2 to 1 μm, small fibres from 1 to 6 μm, and large fibres from 6 to 24 μm. In the five different left connectives examined, the fine fibres numbered from 2006 to 8535 and composed from 56·5 to 83 per cent of the total fibres. The small fibres numbered from 1269 to 2361 and composed from 16·5 to 41 per cent of the total fibre number. The large axons ranged between 29 and 220 in number which represented from 0·5 to 2·5 per cent of the fibre population.     

Fine structure and motility of spermatozoa and composition of the seminal plasma in the perch

The fine structure and motility of spermatozoa and the composition of the seminal plasma of the perch Perca fluviatilis are investigated by electron microscopy, computer assisted cell motility analysis (CMA) and biochemical methods. The spermatozoon is asymmetrical as the flagellum inserts mediolateral on the nucleus. It lacks an acrosome, has an ovoid head and a small midpiece with one mitochondrion. Sperm motility–initiated in distilled water (10° C)–is characterized as follows: 85·0 ± 2·7% of the spermatozoa are motile, the main swimming type (10 ± 1 s after motility initiation) is the linear motion (61·4 ± 24·4%) and the average swimming velocity is 122·4 ± 21·9 μm s^–1. When motility is initiated with NaCl, glucose or sucrose solutions of 100 mosmol kg^–1 the percentage of motile spermatozoa and the swimming types are similar as in water, but the swimming velocity (174·0 ± 22·3 μm s^–1) is significantly higher. Motility is inhibited by high osmolality of the diluent: when increasing the osmolality of the saline solutions to 350 mosmol kg^–1 sperm motility is totally suppressed while potassium (10–40 mmol 1^–1) does not affect motility parameters. pH optimum for sperm motility is between pH 7·0 and 8·5. The seminal fluid contains 124·01 ± 21·68 mmol 1^–1 sodium, 10·22 ± 1·11 mmol 1^–1 potassium and 0·72 ± 0·26 mmol 1^–1 calcium. pH is 8·25 ± 0·09, and osmolality 283·90 ± 37·19 mosmol kg^–1. The following organic components were determined: monosaccharides (glucose 63 ± 19 μmol 1^–1, fructose 54 ± 28 μmol 1^–1, galactose 59 ± 25 μmol 1^–1), lipids (cholesterol 5·51 ± 6·42 μmol 1^–1, triglycerides 72 ± l00 μmol l^–1, cholesteryloleate 15–150 μmol 1^–1, phosphatidylcholine 26 · 31 μmol 1^–1, glycolipids 1–10 mg 100 m1^–1), lactate 108 ± 99 μmol 1^–1, hydroxybutyrate 102 ± 99 nmol 1^–1, choline 59 ± 159 μmol 1^–1, protein 344·75 ± 59·06 mg 100m1^–1, enzymes (β-d -glucuronidase l.4 ± 0.7 μmol h^–1 100 ml^–1, protease (caseolytic activity) 1·0 ± 0·6 μmol h^–1 100 ml^–1, alkaline phosphatase 2520·0 ± 861·0 μmol h^–1 100 ml^–1, acid phosphatase 44.0 ± 16.0 μmol h^–1 100 ml^–1, glucose-6-phosphate dehydrogenase 38·9 ± 86·9 μmol h^–1 100 ml^–1, lactate dehydrogenase 134·4 ± 69·6 μmol h^–1 100 ml^–1, butyrylcholine esterase 0·014 ± 0·010 μmol h^–1 100 ml^–1, adenosine triphosphatase 562·8 ± 665·4 μmol h ^–1 100 ml^–1).     

Native bare zone assemblage nucleates myosin filament assembly

Native myosin filaments from rabbit psoas muscle are always 1·5 μm long. The regulated assembly of these filaments is generally considered to occur by an initial antiparallel and subsequent parallel aggregation of identical myosin subunits. In this schema myosin filament length is controlled by either a self-assembly or a Vernier process. We present evidence which refines these ideas. Namely, that the intact myosin bare zone assemblage nucleates myosin filament assembly. This suggestion is based on the following experimental evidence. (1) A native bare zone assemblage about 0·3 μm long can be formed by dialysis of native myosin filaments to either a pH 8 or a 0·2 m-KCl solution. (2) Upon dialysis back to 0·1 m-KCl, bare zone assemblages and distal myosin molecules recombine to form 1·5 μm long bipolar filaments. (3) The bare zone assemblage can be separated from the distal myosin molecules by column chromatography in 0·2 m-KCl. Upon dialysis of the fractionated subsets back to 0.1 m-KCl, the bare zone assemblage retains its length of about 0·3 μm. However, the distal molecules reassemble to form filaments about 5 μm long. (4) Filaments are formed from mixes of the isolated subsets. The lengths of these filaments vary with the amount of distal myosin present. (5) When native filaments, isolated bare zone assemblages or distal myosin molecules are moved sequentially to 0·6 m-KCl and then to 0·1 m-KCl. the final filament lengths are all about 5 μm. The capacity of the bare zone assemblage to nucleate filament assembly may be due to the bare zone myosin molecules, the associated M band components or both.     

A simple and novel method for recovering adenovirus 41 in small volumes of source water

Aim: A new procedure was developed to recover adenovirus 41 in small volumes (1 l) of water samples based on adsorption, elution and evaporation. Methods and Results: One litre of source water seeded with adenovirus 41 was adjusted to pH 3·5 and filtered using a large pore size (8·0 μm) negatively charged membrane filter (SCWP, 47 mm diameter, made of mixed‐cellulose esters). Then, the filter was eluted using 4 ml of 1·5% beef extract plus 0·75% glycerol (pH 9·0). The eluate was reconcentrated to 0·1 ml or less volumes through evaporation assisted with air flow and heating at 55°C. Recovery of adenovirus 41 reached 55% under tested conditions and reduced filtration time by 85% in contrast to the widely used small pore size filter (0·45 μm pore size, 47 mm diameter). Reconcentration by evaporation achieved approx. 86·8% recovery from source water in approx. 1 h at no cost. Conclusion: The virus concentration method developed in this study is simple and cost‐effective and can be used to efficiently recover adenovirus 41 from turbid water samples. Significance and Impact of the Study: The procedure developed can be applied to detect adenovirus 41 in source water within hours of sampling. In addition, this is the first application of evaporation to concentrate viruses in water samples.     

Enantiomeric resolution by HPLC of axial chiral amides using amylose tris[(S)-1-phenylethylcarbamate]

The enantiomeric resolution of a series of N-arylamides was examined on amylose tris[(S)-1-phenylethylcarbamate] coated onto aminopropylated 7 μm silica with 500 Å diameter pores and on naked silica 5 μm particle size with 500 Å diameter pores. The enantiomeric resolution obtained for this series was excellent on both columns. The enantioselectivity of cellulose and amylose tris (3,5-dimethylphenylcarbamate) coated onto APS-Hypersil (120 Å pore size, 5 μm particle size) was also investigated for this series of compounds. Chirality 9:109–112, 1997. © 1997 Wiley-Liss, Inc.     

Limnological studies on some lakes in the Netherlands

Most Dutch lakes are small and shallow, resulting from peat dredging since the late 18th century. However, deep lakes have appeared recently owing to sand digging. Limnological features of one such lake, Wijde Biik (N. Holland), were studied during 1968–70. The lake with an average depth of 11 4 m (maximum depth 31 m) and area of 2·65 × 10⁶m² is one of the deepest and biggest in the Loosdrecht-lakes area. The lake is 125 cm below sea level, and underground water-movements play an important part in the lake's hydrology. The lake exhibits thermal stratification on warm and calm days; since the lake surroundings are open and flat, wind and nocturnal cooling destroy such a stratification. There is continuous circulation from autumn through spring. The O2 saturation (%) in the upper water varies from 70 to 120%. Bottom waters were never anaerobic (lowest values 10% O₂ saturation). CI^? (2·8m-equiv.) and HCO^?₃ (1·9 m-equiv.) were the dominant anions just as Ca⁺⁺ (2·77 m-equiv.) and Na⁺ (2·5 m-equiv.) formed the main cations. Chlorides have increased 2·5-fold in the 40 years as a geochemical consequence of deepening. The surface drainage has minor influence on lake's water chemistry. Part-P (10–140 μg/I) and PO₄-P (2–40 μg/1) recorded maximum and minimum respectively, and NO₃-N (0·05–1·15 mg/1) its minimum, during Microcystis abundance in August 1968. The SiO₂-Si decreased from February 1969 (400 μg/l) to June 1969 as Diatotna elongatum increased. The Si-decrease to <30% of the 1932 values is due to removal of Si-rich clay and silt, due to sand digging. Chlorococcales were the important lake algae. Desmids were poor. Microcystis dominated as a rule from July-September, achieving from 15 to 31 colonies/ml. Poor light transmission rather than nutrients limits plankton growth as also the primary production in the lake. Copepoda were the dominant zooplankton. Bosmina coregoni recorded between 2 and 44 individuaIs/1 in summer 1968 and was the main cladoceran. The average primary production during summers of 1969 and 1970 was 380 and 497 mg C m^?2 day^?1 respectively. Light limited production below 1 m—1 % light in 1969 and 10% in 1970 penetrated down to 4 m. About 70% of the production took place in the upper 2 m. Calculation of production according to theoretical models under-estimated the observed values by 12% because Z_0·5Ik lay much above (0·8–2·8 m) the expected value of 3·5 m. It is suggested that in turbid lakes like Wijde Blik in situ incubations should be done at 0·5 m intervals in the upper 2 or 3 m.     

DIFFUSION THROUGH STOMATES

Ting, Irwin P., and Walter E. Loomis. (Iowa State U., Ames.) Diffusion through stomates. Amer. Jour. Bot. 50(9): 866–872. Illus. 1963.—It is shown that the rule that diffusion through isolated, small pores is proportional to the diameter rather than the area of the pores is valid for pores of diameters as small as 20 μ, and that the curve extends to the origin at zero diameters, indicating that the law is effective throughout the range of stomatal sizes. Suggestions that an elliptical pore will be relatively more effective in diffusion than a circular one and that diffusion is concentrated at the periphery of the pore are not supported by experimental evidence and are physically improbable. Brown and Escombe's conclusion that there is no interference in the diffusion through the individual pores of a multiperforate membrane if the pores are spaced 10 diameters apart is not valid for diffusion through the stomates of a leaf. With pores of 200 μ and less spaced 10 diameters apart, interference increases rapidly with a smaller size and larger number of pores. As a result, the diffusion through a membrane with pores 19 μ in diameter and 190 μ apart was the same as that through a membrane with pores 132 μ in diameter and 1.32 mm apart, although the calculated capacity of the first membrane was 7 times that of the second. The diffusion of water vapor through multiperforate membranes with pores spaced 10 diameters apart has an apparent maximum of 65–70% of the diffusion through an open tube. Calculations of the effect of partial closing of stomates, using Verduin's equation for interference between pores, indicate that the theoretical diffusion capacity of 10 μ stomates spaced at 10 diameters would be increased several times by closing to an average diameter of 5 μ. This increase illustrates the dominant effect of interference in diffusion through small, closely spaced pores. Calculated diffusion through these stomates would not be decreased until they were more than 95% closed. It is concluded that stomatal opening will have no important effect on diffusion from or into a leaf until the stomates are essentially closed.     

Fine structure of the alary muscles of the American cockroach

The alary muscles of the cockroach, Periplaneta americana, are striated with an A-band of 3·0 to 3·5 μm long. Each muscle fibre was 10 to 12 μm in diameter and Z-lines appeared as small discrete units staggered throughout the sarcoplasm. Mitochondria were conspicuously located near the Z-line areas and were absent from the middle portion of the sarcomere. A transverse membrane system was present which formed dyad structures with a relatively sparse sarcoplasmic reticulum. Cockroach alary muscles were innervated by axons containing electron-dense granules of near 100 nm in diameter. These are thought to be typical of ‘neurosecretory’ axons based on their ultrastructural appearance.     

Micro sprayers for the laboratory application of pesticides

The microtip nozzle assembly described by Uk (1978) has been modified to provide a reliable and versatile sprayer for the laboratory application of pesticide formulations. The improved performance has been achieved through the introduction of knurled thimbles giving controlled adjustment of needle and stylus settings and by the provision of an offset liquid reservoir (0·1–2 ml) either pressurised or non-pressurised. The device, which delivers monosize droplets (in-flight diameter 50–500 μm) at velocities ranging from 0·5–20 m s^-1 has been used for aqueous and oil solutions, water dispersible powders and emulsifiable concentrates of varying concentration (0·1-30g a.i. litre^-1) and is particularly suitable for the application of radiolabeled chemicals.     

Dispersal of Septoria nodorum Pycnidiospores by Simulated Rain and Wind

The influence of wind on the splash dispersal of Septoria nodorum pycnidiospores was studied in a raintower/wind tunnel complex with single drops or simulated rain falling on spore suspensions or infected stubble with windspeeds of 1.5 to 4 m/sec. When single drops fell on spore suspensions (depth 0.5 mm, concentration 7.8 × 10⁵ spores/ml) most of the spore-carrying droplets collected on fixed photographic film between 0–4 m downwind (windspeed 3 m/sec) were >200 μm in diameter. However, most spores were carried in droplets with diameter > 1000 μm, 70 % of which carried more than 100 spores. When simulated rain fell on infected stubble most of the spore-carrying droplets collected beyond 1 m downwind (windspeeds 1.4 and 4 m/sec) were <200 μm in diameter and none were >600 μm; most of these droplets carried only one spore. The distribution of splash droplets (with diameter >100 μm) deposited on chromatography paper showed a maximum at 40–50 cm upwind of the target but many more droplets were deposited 20–30 cm downwind, when single drops fell on a spore suspension (concentration 1.2 × 10⁵ spores/ ml) containing fluorescein dye with a windspeed of 2 m/sec; droplets were collected up to 3 m downwind but not more than 70 cm upwind. With a windspeed of 3 m/sec, numbers of sporecarrying droplets and spores collected on film decreased with increasing distance downwind; most were collected within 2 m of the target but some were found up to 4 m. When simulated rain fell on infected stubble, increasing the windspeed from 1.5 to 4 m/sec greatly increased the number of spores deposited more than 1 m downwind. At 1.5 m/sec none were collected beyond 2 m downwind, whereas at 4 m/sec some were collected at 4 m. A few air-borne S. nodorum spores were collected by suction samplers at a height of 40 cm at distances up to 10 m downwind of a target spore suspension on which simulated rain fell.     

Dispersal of Rhynchosporium secalis conidia from infected barley leaves or straw by simulated rain

Simulated rain (mean drop diameter c. 1 or 3 mm) was allowed to fall for 10 – 15 min on to barley leaves or straw infected by Rhynchosporium secalis (leaf blotch). The leaves were supported on a mesh through which run-off water drained and the straw was supported on a rigid surface on which run-off water collected. The numbers of R. secalis conidia and spore-carrying splash droplets collected by horizontal samplers (microscope slides and pieces of photographic film) decreased rapidly with increasing distance from and increasing height above the sources, with half-distances of 2 – 10 cm. Less than 10% of the spores or droplets reached heights of more than 30 cm. Incident drops 3 mm in diameter produced more spore-carrying droplets and dispersed more conidia than did 1 mm drops. The size category of splash droplets with the greatest proportion of the spore-carrying droplets dispersed by 3 mm drops was 200 – 400 μm, whether the source was infected barley leaves or barley straw. For leaves or straw the greatest proportions of spores were carried in droplets > 1000 μm in diameter. The mean diameter of spore-carrying droplets (478 μm) dispersed from free-draining leaves was less than that of droplets from straw plus run-off water (563 μm). However, the leaf source had more spores cm^-2 and the mean number of spores per droplet was greater (113 as opposed to 6·8) than for the straw source.     

Influence of oil shale on intertidal organisms: Effect of oil shale extract on settlement of the barnacle Balanus balanoides (L.)

As part of a study to investigate the effect of oil seeps on intertidal organisms, oil extracts of Blackstone oil shale from Kimmeridge on the Dorset coast were used in laboratory experiments to test their effect on the settlement of the barnacle Balanus balanoides (L.). Thin films of oil extract painted on the surface of pits in slate panels had no effect on cyprid settlement when applied up to a surface density of 2.8 g · m^?2, representing a thickness of 3.3 μm. Larger surface densities of oil stimulated cyprids to settle in far greater numbers than on unoiled panels. The maximum effect was obtained at a surface density of between 14.0 and 56.0 g · m ^?2, representing a thickness of 16.5 μm and 66.0 μm. With higher concentration of oil in the pits, stimulation to settle was reduced although cyprid settlement was still encouraged at a surface density of oil of 112g · m^?2 or 132 μm thickness.The unfractionated crude oil shale extract was a less powerful stimulus for barnacle settlement than a partially purified solution of the integumental protein arthropodin, another strong settlement inducer for barnacle cyprids.     

RNA synthesis in imaginal disks of Galleria mellonella: Effects of alpha- and beta-ecdysone and fat body in vitro

The effects of alpha-ecdysone (α-E), beta-ecdysone (β-E), and larval fat body on morphogenesis and total RNA synthesis in wing imaginal disks of Galleria mellonella were studied. Both ecdysones induce morphogenesis of disks in vitro. Alpha-ecdysone and β-E (0·3–3·0 μg/ml) stimulate RNA synthesis 30 and 60 per cent above control levels, respectively. While less α-E (0·3 μg/ml) is required to increase RNA synthesis than to induce morphogenesis, the reverse is true for β-E. Morphogenesis (i.e. tracheole migration and evagination) can proceed in the presence of concentrations of β-E (0·03 μg/ml) that are subthreshold for the induction of RNA synthesis (0·3 μg/ml). We conclude, therefore, that the increase in total RNA (presumbly ribosomal) is unrelated to and not a prerequisite for tracheole migration or evagination. If morphogenically active preconditioned medium (i.e. medium in which α-E and fat body have been incubated for 48 hr and the fat body then removed) is added to disk cultures, RNA synthesis is not stimulated. Apparently, increases in total RNA caused by both ecdysones may not be necessary for early in vitro disk development. The independent nature of some ecdysone-induced events and implications of our conclusions are discussed.     

Comparative toxicity of the two anti-coagulants, coumatetralyl and warfarin, to wild house-mice (Mus musculus L.)

In comparative tests using individually caged wild house-mice (Mus musculus L.) coumatetralyl at 0·05 % in an oatmeal bait-base was found to be as acceptable as plain bait and as acceptable and as toxic as warfarin at 0·025% (the standard dosage). It was less readily accepted at 0·1 or 0·2% in the same bait-base or at 0·05% in a proprietary bait formulation. In further tests with suspected warfarin-resistant mice, coumatetralyl at either 0·05, 0·1 or 0·2% proved more toxic than warfarin at either 0·025, 0·1 or 0·2% respectively. However, some individuals survived 21 days feeding on each of these concentrations of coumatetralyl and, in field and laboratory trials, 0·05 and 0·1% coumatetralyl baits failed to control warfarin-resistant mouse populations after 3–5 weeks. It is concluded that coumatetralyl is a suitable alternative poison to warfarin for use against mice that are susceptible to anti-coagulants but that it is unlikely to control warfarin-resistant populations effectively.     

Boundaries between soil compartments formed by microporous hydrophobic membranes (GORE-TEXR) can be crossed by vesicular-arbuscular mycorrizal fungi but not by ions in the soil solution

Various container systems have been described in which soil regions available to hyphae only are separated from the mycorrhizal root region by 30–60 m mesh screens to study nutrient exchange between plants and fungi in the mycorrhizal symbiosis. The screens designed up to now prevent penetration by roots but allow easy passage of fungal hyphae as well as diffusion or mass flow of water and nutrient solutions. We tested hydrophobic microporous polytetrafluorethylene (PTFE) membranes (GORE-TEX^R) with 5 to 15 m diameter pores in an attempt to obtain a better seal between compartments and to prevent uncontrolled nutrient transport by diffusion or mass flow. We found that these membranes completely prevented diffusion or mass flow of ions between two soil compartments but could be penetrated easily by the vesicular-arbuscular mycorrhizal fungus Glomus mosseae, as demonstrated by the rapid colonization of soybean roots (Glycine max L.) from an inoculum across the membranes.     

Elongation of rod-shaped bacteria.

Three models relating cell length to generation time are considered for rod-shaped bacteria growing under steady-state conditions; all three presuppose linear elongation. The first model assumes that the rate of elongation is proportional to the instantaneous number of chromosome replication forks per cell; the others, that it is inversely related to the generation time and doubles a fixed time prior to cell division. One of these (model 2) treats this relationship as continuous, with the doubling occurring during the last division cycle (at chromosome termination), while the other is a discrete model in which the doubling in rate takes place at chromosome initiation. Expressions are derived for mean cell length and length at birth in each case.Comparison with experimental data on E. coli B/r using non-linear least-squares techniques results in an excellent fit for model 2 and unsatisfactory ones for the others, the best estimate for the time at which the rate doubles being 15·3 min prior to cell division and for the minimum length at birth (i.e., as the growth rate of the culture tends to zero), 1·47 μm.The functional relationship between cell radius and generation time implied by model 2 is also presented. This model again produces a good fit to the experimental data and provides, for the first time, a direct estimate of the volume/origin ratio at initiation of chromosome replication 0·35 ± 0·05 μm³ (s.e.).The results obtained here are compared with various qualitative observations reported in the literature and with such numerical data as are available.