Quantitative Mineralbestimmung in der Schlufffraktion von Böden auf der Grundlage der chemischen Analyse und unter Anwendung der Karl-Fischer-Titration. I. Verfahren

Quantitative estimation of the mineralogical composition of silt fractions of soils based on both, chemical analysis and application of Karl-Fischer-titration. I. Method This paper describes a method for calculating the mineralogical composition of the silt fractions of soils. The chemical analysis and the temperature dependence of water release are used for determining micas and feldspars, each in three components in a relatively short procedure. The release of water was measured by Karl-Fischer-titration at controlled temperatures. At temperatures above 550°C the water release of the particle size fractions correlates with their content of micas. The quantity of micas can be obtained from the amount of released water and the results of the chemical analysis. The influence of kaolinite, amphibole and the fluoride content on the calculation is described. By considering the potassium content of the mica fraction results of the chemical analysis are used to quantify feldspars.     

Potential for Asexual Propagation of Several Commercially Important Species of Tropical Sea Cucumber (Echinodermata)

Six species of tropical sea cucumbers (Echinodermata) of high to moderate commercial value were evaluated as to their potential for being propagated asexually by induction of transverse fission. The species considered were Thelenota ananas, Holothuria fuscogilva, Actinopyga mauritiana, A. miliaris, Stichopus chloronotus , and S. variegatus . Rubber bands placed midbody on the sea cncumbers provided an effective yet simple technique to induce transverse fission. Although fission could be induced in all six species, only T. ananas and S. chloronotus had the ability to regenerate both anterior and posterior parts into whole animals. Other species showed no or low potential for regeneration ( H. fuscogilva, A. mauritiana ) or regeneration of only the posterior part into whole animals ( S. variegatus, A. miliaris ). Both T. ananas and S. chloronotus had survivorship of nearly 80% or greater. S. chloronotus regenerated anterior and posterior parts into whole animals within 3 mo. In contrast, T. ananas regenerated the posterior part into a whole animal within 5 mo while the anterior part was regenerated within 7 mo. Consequently, weight recovery began earlier with S. chloronotus relative to T. ananas .     

Morphometric analysis of the retina from horses infected with the Borna disease virus

Borna disease (BD) is a fatal disorder of horses, often characterized by blindness. Although degeneration of retinal neurons has been demonstrated in a rat model, there are controversial data concerning whether a similar degeneration occurs in the retina of infected horses. To investigate whether BD may cause degeneration of photoreceptors and possibly of other neuronal cells at least at later stages of the disease, we performed a detailed quantitative morphologic study of retinal tissue from Borna-diseased horses. BD was diagnosed by detection of pathognomonic Joest-Degen inclusion bodies in the postmortem brains. Paraffin sections of paraformaldehyde-fixed retinae were used for histologic and immunohistochemical stainings. Numbers of neurons and Müller glial cells were counted, and neuron-to-Müller cell ratios were calculated. Among tissues from 9 horses with BD, we found retinae with strongly altered histologic appearance as well as retinae with only minor changes. The neuron-to-Müller cell ratio for the whole retina was significantly smaller in diseased animals (8.5 +/- 0.4; P < .01) as compared with controls (17.6 +/- 0.8). It can be concluded that BD in horses causes alterations of the retinal histology of a variable degree. The study provides new data about the pathogenesis of BD concerning the retina and demonstrates that a loss of photoreceptors may explain the observed blindness in infected horses.     

Photonic crystal light collectors in fish retina improve vision in turbid water

Despite their diversity, vertebrate retinae are specialized to maximize either photon catch or visual acuity. Here, we describe a functional type that is optimized for neither purpose. In the retina of the elephantnose fish (Gnathonemus petersii), cone photoreceptors are grouped together within reflecting, photonic crystal-lined cups acting as macroreceptors, but rod photoreceptors are positioned behind these reflectors. This unusual arrangement matches rod and cone sensitivity for detecting color-mixed stimuli, whereas the photoreceptor grouping renders the fish insensitive to spatial noise; together, this enables more reliable flight reactions in the fish's dim and turbid habitat as compared with fish lacking this retinal specialization.