Thick bone section preparation using a silicon-rubber-based sealant

A method has been developed, using a silicon-rubber-based sealant, which allows 2–3-mm-thick specimens to be maintained in a protected fluid environment for a number of months, without risk of dehydration. Following this, the specimen can be retrieved, stained, embedded and sectioned further. For example, 2-mm-thick sections of fixed unstained bone are easily examined by means of epi-illuminated polarized light and fluorescence microscopies using either conventional or confocal optics. The method could easily be extended to other tissues, for example brain tissue.     

Estimation of individual feature surface area with the vertical spatial grid

The area of an individual bounded surface (e.g. the boundary of a properly sampled cell) can be estimated from an isotropic uniform random stack of parallel sections, or of non-invasive planar scans, using the well-known spatial grid. A standing problem was to estimate the area of an individual bounded surface with an arbitrary degree of accuracy from a vertical (i.e. not isotropic) stack of sections or scans. A new tool to do this, called the ‘vertical spatial grid’, is presented.     

On asymmetric stochastic bang-bang control†

Three stochastic bang-bang control problems, the predicted miss, the linear regulator, and a complete observation model, are shown to have formally similar solutions under an asymmetric boundedness condition on the control u(t), 0<t<T.     

Verification of cell viability at progressively higher scanning forces using a hybrid atomic force and fluorescence microscope

Dry 40× and 60× microscope objectives were fitted with opaque black masks in order to eliminate reflection and scattering of light off the objective front lens assembly during oblique incidence reflection (OIR) microscopy. The reflection and scattering are shown to induce background glare that leads to degradation in the quality of the OIR images. Mask prototypes were designed and machined to snap onto the spring-loaded retractable front lens assembly of each objective. OIR images of live cells and normalized intensity line profiles are used to demonstrate that, if these alterations to the housing of the objective are implemented, background glare is significantly reduced with the 60× objective, and virtually eliminated with the 40× objective.     

ANTIMICROBIAL ACTIVITY OF SOME FOOD FLAVORING COMPOUNDS

Of 21 food flavoring compounds tested against 39–40 organisms, 10 were ineffective at 1,000 ppm or 10 mM either at pH 6 or 8 and by either surface plating or in broth. The 11 effective compounds were d- and l-carvone, diacetyl, ethyl vanillin, eugenol, maltol, menthol, phenylacetic acid, phenylacetal-dehyde, 2,3-pentanedione and vanillin; with diacetyl and eugenol being the most effective. All were more effective at pH 6 than at pH 8. With the exception of maltol and phenylacetic acid, each was generally more effective against fungi than bacteria with the lactic acid bacteria being the most resistant. At pH 5.5 and 5°C, diacetyl was inhibitory to Pseudomonas fluorescens and P. geniculata at < 10 ppm. The findings suggest that compounds used in acid foods, ostensibly as flavoring agents, may exert antimicrobial effects when considered in context with all parameters of growth.     

HEXOSAMINE PRODUCTION BY PSYCHROTROPHIC FOOD-SPOILAGE BACTERIA UNDER VARYING GROWTH CONDITIONS

Four psychrotrophic, gram negative meat isolates were grown at 6 and 22°C with and without aeration, in AOAC synthetic broth with 0.1% glucose and in a basal medium containing 0.1% glucose and 0.5% glycine (BMGG-1). In AOAC broth, three strains produced more hexosamine at 6°C, while the fourth produced more at 22°C. Three of the four strains also produced more slime at 6°C. All four strains grew faster with aeration at both temperatures, but produced less hexosamine. Under all conditions, the growth rate of each strain was inversely proportional to its hexosamine production. During the growth cycle in BMGG-1, medium pH dropped until the log phase was under way and then rose again through the stationary phase. This rise coincided with the depletion of glucose. Hexosamine production first became detectable at the end of the log phase, rose during the stationary phase, and then leveled off. Adjusting pH to prevent the initial drop increased both growth and hexosamine production. Raising the concentration of glucose to 0.5% accelerated growth but decreased hexosamine production. Approximately 95.1% of the hexosamine produced was cell-associated. It consisted primarily of glucosamine polymers with a lesser amount of galactosamine. Only 3.0% of the nitrogen from the BMGG-1 was utilized by the cells. Of this 3.0%, 58% was used for ammonia, 27.2% for hexosamine, and 14.8% for other substances. Of the 40.7% used for total cell production, 63.8% went into hexosamine.