Patterns of oxygen consumption during establishment of cephalocaudal polarity in the early chick embryo.

Oxygen uptake was studied during the establishment of cephalocaudal polarity in the very early chick embryo, i.e., 10 hr before (stage VI) and at laying (stage X). Oxygen fluxes in minute regions of the intact blastoderms were measured in vitro by scanning microspectrophotometry in the presence or absence of glucose. The oxygen consumption of the whole blastoderm remained constant (6 nmol O2 X hr-1) throughout the period studied, although the number of cells increased more than twofold. The regional oxygen fluxes varied from 0.41 to 1.13 nmol O2 X hr-1 X mm-2 at stage VI and from 0.42 to 0.70 nmol O2 X hr-1 X mm-2 at stage X. At stage VI, the oxygen flux in the center of the blastoderm was significantly higher than that in its periphery. This pattern remained evident when the values were corrected for cell number or for cytoplasmic volume. At stage X, there was a tendency for the oxygen fluxes to decrease from the posterior to the anterior regions of the area pellucida. Thus the pattern of oxidative metabolism in the late uterine embryos seems to change from radial to bilateral. This change of symmetry probably reflects the process of formation of the embryonic axis. In addition, the fact that the oxygen uptake was similar in the presence or absence of glucose suggests that early chick embryos metabolize essentially intracellular stores.

A comparative study of ballpoint ink ageing parameters using GC/MS.

For more than a decade scientists tried to develop methods capable of dating ink by monitoring the loss of phenoxyethanol (PE) over time. While many methods were proposed in the literature, few were really used to solve practical cases and they still raise much concern within the scientific community. In fact, due to the complexity of ink drying processes it is particularly difficult to find a reliable ageing parameter to reproducibly follow ink ageing. Moreover, systematic experiments are required in order to evaluate how different factors actually influence the results over time. Therefore, this work aimed at evaluating the capacity of four different ageing parameters to reliably follow ink ageing over time: (1) the quantity of solvent PE in an ink line, (2) the relative peak area (RPA) normalising the PE results using stable volatile compounds present in the ink formulation, (3) the solvent loss ratio (R%) calculated from PE results obtained by the analyses of naturally and artificially aged samples, (4) a modified solvent loss ratio version (R%*) calculated from RPA results. After the determination of the limits of reliable measurements of the analytical method, the repeatability of the different ageing parameters was evaluated over time, as well as the influence of ink composition, writing pressure and storage conditions on the results. Surprisingly, our results showed that R% was not the most reliable parameter, as it showed the highest standard deviation. Discussion of the results in an ink dating perspective suggests that other proposed parameters, such as RPA values, may be more adequate to follow ink ageing over time.