On the removal and quantification of algal aufwuchs from macrophyte hosts

Accurate population density measurements of algal aufwuchs associated with macrophyte hosts appears to be fraught with uncertainties. This account details a procedure involving aufwuchs removal by agitation and acid hydrolysis with subsequent quantification by a special Sedgwick-Rafter cell counting technique. The aufwuchs removal efficiency from five hosts of widely differing morphology was calculated to be 98.0% (95% confidence limits: 96.3%, 99.7%) after five 45 second agitation cycles.     

Sequence diversity among related genes for recognition of specific targets in DNA molecules

Escherichia coli strains K12 and B, and a new strain designated D, each encode a characteristic restriction and modification enzyme. These enzymes (EcoK, EcoB and presumably EcoD) comprise three subunits of which one, that encoded by the so-called specificity gene (hsdS), is responsible for recognition of the DNA sequence specific to that system. The other two subunits, encoded by hsdR and hsdM, are interchangeable between systems, and the available molecular evidence suggests that the hsdR and hsdM genes are highly conserved. The DNA sequence of a segment of the hsd region that includes the hsdS gene has been determined for each of the three strains. The hsdS gene varies in length from 1335 to 1425 base-pairs and the only regions showing obvious homology, one of about 100 base-pairs and a second of about 250 base-pairs, are highly conserved. The remainder of each hsd S gene shares little, or no, homology with either of the other related specificity genes. Thus, the specificity subunits, though components of a family of closely related enzymes with very similar functions, have remarkably dissimilar primary structure.     

Correlation between clinical and autopsy diagnoses in a community hospital

Forty-six consecutive autopsies performed in 1 year on patients who died in a 120-bed urban community hospital were analysed with respect to clinical-pathological correlation. The mean age of the patients was 71 years. Errors in clinical diagnosis were assigned to one of four classes: class I, a missed major diagnosis, the detection of which before death would probably have changed management and resulted in longer survival or possible cure; class II, a major missed diagnosis that, if detected before death, would probably not have altered management; and classes III and IV, minor missed diagnoses. Six (13%) class I and 10 (22%) class II errors were found, as well as a number of class III and IV errors. Suggestions are made regarding the use of such data in audit procedures.     

Morphology of the core fibrous layer of the cetacean tail fluke

The cetacean tail fluke blades are not supported by any vertebral elements. Instead, the majority of the blades are composed of a densely packed collagenous fiber matrix known as the core layer. Fluke blades from six species of odontocete cetaceans were examined to compare the morphology and orientation of fibers at different locations along the spanwise and chordwise fluke blade axes. The general fiber morphology was consistent with a three‐dimensional structure comprised of two‐dimensional sheets of fibers aligned tightly in a laminated configuration along the spanwise axis. The laminated configuration of the fluke blades helps to maintain spanwise rigidity while allowing partial flexibility during swimming. When viewing the chordwise sectional face at the leading edge and mid‐chord regions, fibers displayed a crossing pattern. This configuration relates to bending and structural support of the fluke blade. The trailing edge core was found to have parallel fibers arranged more dorso‐ventrally. The fiber morphology of the fluke blades was dorso‐ventrally symmetrical and similar in all species except the pygmy sperm whale (Kogia breviceps), which was found to have additional core layer fiber bundles running along the span of the fluke blade. These additional fibers may increase stiffness of the structure by resisting tension along their long spanwise axis.     

Sedgwick-rafter cell counts: a procedural analysis

Information in the existing literature on some aspects of the collection and statistical analysis of Sedgwick-Rafter cell data appears contradictory, confusing, or absent. Using data from an experimental phytoplankton population as a basis, an investigation of S-R cell procedure has been undertaken with the following conclusions: I) settling time depends upon the type of preservation and the composition of the sample; 2) the field counting technique gives more accurate data and is less time consuming than the strip counting technique; 3) making fewer counts on each of a greater number of S-R cells gives more accurate results than making a greater number of counts on one or several S-R cells; 4) nonparametric methods offer a more convenient and nearly as efficient a means of detecting statistically significant differences as compared with parametric methods. A method is presented for optimally allocating counts within and among S-R cells for getting an estimator with the greatest precision in the least time.