Nitrogenase activity of Rhizobium sp. strains in pure culture in relation to extracellular polysaccharide composition and antigenic affinity.

Five strains of slow-growing Rhizobium sp. (strains CB756, 32HI, CB562, CB627 and QA549) out of seventy examined developed appreciable nitrogenase activity in pure culture. CB756 and 32HI were serologically indistinguishable and each produced 6-deoxy-L-talose as a major component of its extracellular polysaccharide. They did not share these properties with CB562, CB627 or QA549.     

Physiological stress responses to confinement in diploid and triploid Atlantic salmon

Confinement of juvenile Atlantic salmon Salmo salar from four different populations (all–female diploids, all–female triploids, mixed sex diploids and mixed sex triploids) either before (FW parr) or after (SW smolts) transfer to sea elevated plasma cortisol and plasma lactate from control levels irrespective of ploidy status. Both before and after confinement, plasma cortisol levels in SW smolts (6–174 ng ml^–1) were higher than those in FW parr (4–58 ng ml^–1), which possibly reflected the physiological challenge of acclimation to SW. Mixed sex populations of SW smolts had higher cortisol levels than all–female populations. The duration of confinement (1, 3 or 6 h) affected the magnitude of the plasma cortisol and lactate responses in SW smolts. Plasma cortisol levels in diploid and triploid SW smolts subjected to 2 h of confinement decreased to pre–stress levels within 6 h post–confinement. Plasma lactate levels were not significantly different from pre–stress levels 48 h after confinement. As no difference exists in primary and secondary stress responses of Atlantic salmon of differing ploidy status, it is unlikely that differences in mortality rates between diploid and triploid populations under commercial conditions can be attributed to differences in their physiological responses to periods of stress lasting up to 6 h.     

A Spot Test for Catechol 2:3-Oxygenase in Bacteria

A simple and quickly performed colour test is described, in which organisms containing catechol 2:3-oxygenase (meta-pyrocatechase) produce from catechol a yellow coloured intermediate, α-hydroxymuconic semialdehyde. The yellow colour is produced most consistently, rapidly and intensely by 2–4 day old cultures from 2·7–27 mM solutions of catechol. The purple-brown colour produced by some organisms is discussed.
Using growth from nutrient agar plates, the test was applied to cultures of 239 Gram negative bacteria; all of the 64 cultures which gave a positive result had been in contact previously with aromatic substrates and many of them could oxidize phenol. The significance of a positive reaction is discussed briefly.     

Changes in vision and olfaction during sexual maturation in the European eel Anguilla anguilla (L.)

Retinal structure was examined in sexually immature and artificially matured female Anguilla anguilla . Inner nuclear layer cell numbers decreased from 600 mm⁻¹ retinal cross-section to 300 mm^−I and ganglion cells from 60 to 30 mm⁻¹ cross-section, during sexual maturation. Most of the decrease occurred prior to the stage of maturation at which migration begins. Electroretinograms were recorded from the intact eyes of immature and maturing eels. There was no change in scotopic sensitivities to light of wavelengths 480 and 520 nm, with increasing sexual maturity. Olfactory organs were examined in female eels of a similar range of maturity states and were found to atrophy in artificially matured eels of advanced development. The density of mucous cells in olfactory lamellae decreased from a maximum of 443 mm⁻² in sexually immature eels to as low as 19 mm⁻² in sexually maturing eels. The changes in vision and olfaction were thought to indicate a change in the relative importance of the two sensory modalities with sexual maturation.     

Changes in body musculature with sexual maturation in the European eel, Anguilla anguilla (L.)

The structure and distribution of red and white muscles have been investigated in female Anguilla anguilla of varying sexual maturity. Red muscle volumes increased with sexual maturation from approximately 5% of total muscle volume in sexually immature eels to a maximum of 13.3% in sexually maturing animals. Volume increase was due to increasing fibre diameter rather than recruitment of new fibres. Intracellular volume fractions of lipid and mitochondria increased markedly in maturing fish. Artificially matured cels showed the largest increases in muscle lipid. The possible functional roles of red and white muscle during migration are discussed.     

Multiply imputing missing values arising by design in transplant survival data

In this article, we address a missing data problem that occurs in transplant survival studies. Recipients of organ transplants are followed up from transplantation and their survival times recorded, together with various explanatory variables. Due to differences in data collection procedures in different centers or over time, a particular explanatory variable (or set of variables) may only be recorded for certain recipients, which results in this variable being missing for a substantial number of records in the data. The variable may also turn out to be an important predictor of survival and so it is important to handle this missing-by-design problem appropriately. Consensus in the literature is to handle this problem with complete case analysis, as the missing data are assumed to arise under an appropriate missing at random mechanism that gives consistent estimates here. Specifically, the missing values can reasonably be assumed not to be related to the survival time. In this article, we investigate the potential for multiple imputation to handle this problem in a relevant study on survival after kidney transplantation, and show that it comprehensively outperforms complete case analysis on a range of measures. This is a particularly important finding in the medical context as imputing large amounts of missing data is often viewed with scepticism.     

An improved algorithm for finding diagnostic taxonomic descriptions

A computer program is described which finds sets of diagnostic characters for the recognition of species. Unlike previous algorithms, it finds all the possible sets requested and will also run with reasonable demands on computer time and storage. The program will search for sets with a specified size range and with a given minimum number of diagnostic characters to distinguish a taxon from all the others.     

A package of computer programs for handling taxonomic databases

A package of programs is described which processes taxonomicdata, suitable to use when preparing monographs, handbooks,Floras or Faunas, in which species or other taxa are describedand identified. There is also an interactive program for specimenidentification, and conversion routines which prepare data fornumerical taxonomy (clustering and cladistics). The programsare equally suitable for botany or for zoology, or even fornon-biological data. Received on September 20, 1985; accepted on November 11, 1985