Frequency-dependent mating success among mutant ebony ofDrosophila melanogaster

Summary Measurements of the mating success of wild and ebony strains ofD. melanogaster with different degrees of competition have shown a frequency-dependent effect in both cases, but with a negative correlation for the wild and a positive correlation for the ebony strain.Supported by FAPESP Grant No. 70/049.     

New robertsonian metacentrics in another 22-chromosome mouse population in Central Apennines

Summary New centric fusions (Rb 8-14 Rma) have been described in a 22-chromosome karyotype from a Mus musculus population in southern Central Italy. The diakinesis of hybrids obtained by crossing mice with different 22-chromosome complements show a ring-multivalent made up 16 metacentrics pairing arm-to-arm.     

Effects of CO2 exposure on distribution of various forms of iron and copper in guinea-pig tissues

Summary The effects on iron and copper distribution and metabolism of exposure to high levels of CO₂ were studied in the guinea-pig. Mature, male animals were placed in an atmosphere of 15% CO₂, 21% O₂ (balance N₂), and sacrificed from 1 h to 1 week thereafter. Total iron and copper concentrations of blood, liver, spleen and bone, as well as concentrations of heme and ferritin iron, were measured together with blood hematocrit, reticulocytes, plasma hemoglobin, plasma ceruloplasmin and copper concentrations. The results show clearly that rapid and sustained red cell damage or hemolysis ensued several h from the start of CO₂ treatment. This resulted in loss of iron and copper from the blood, an influx of both elements into liver, spleen and bone, and a rise in plasma ceruloplasmin. Influx of iron into liver and spleen caused an accumulation of ferritin, the main site for iron storage in cells. Following the effect on red cells, there was an accumulation of heme iron, and a decreased hematocrit, best explained by a depressed activity of the reticuloendothelial and erythropoietic systems. A period of adaptation succeeded these events, in which all blood parameters and most tissue values returned to normal, despite the continuing presence of high CO₂. The only changes not reversed were the elevations in liver, spleen and bone iron stores. These remained high, with a net accumulation of >2 mg iron, or 3–4 times more than originally present. The results indicate that at least in the guinea-pig, high CO₂ exposure results in red cell damage and other events leading to an accumulation of additional iron in the body; also, that iron accumulated as ferritin and hemosiderin in liver and spleen may not be readily available to restore blood hemoglobin concentrations on an acute basis.Acknowledgments. We gratefully acknowledge the technical assistance of Joan R. Moor and Lakshmi Vulimiri with these studies, and the support of Grants No. 17249 and HL22410 from the U.S. Public Health Service.     

Behaviour of a guanidine-dependent strain of poliovirus 1 in sucrose density and pH gradients

Riassunto La densità in gradiente di saccarosio ed il punto isoelettrico delle particlle virali di poliovirus guanidino-dipendentri non differiscono da quelle del virus guanidino-sensibile di origine.     

Action of sugars on methionine transfer in ehrlich ascites carcinoma cells

Zusammenfassung Bei mit Zucker aufgeladenen Ehrlich-Ascites-Tumorzellen steigert sich das Eindringen des Methionins in die Zelle. Wenn sich dieselben Zucker im extrazellulären Raum befinden, bleibt dieser Effekt aus. Die möglichen Ursachen dieses Effektes werden besprochen.     

Studies on the cytochemical localization of adenylate-cyclase activity inDugesia lugubris s.l.

Summary The localization of adenylate-cyclase activity inDugesia lugubris s.l. has been investigated cytochemically using 5-adenylyl-imidodiphosphate as substrate. The enzyme was localized in mucous gland cells, in rhabdite cells, in intercellular spaces and also in nerve endings of this planarian. The presence of adenylate-cyclase on the membrane suggests that it might mediate different stimulus-secretion coupling by increasing cyclic AMP synthesis in specialized areas of the planarian.Supported in part by a grant from Consiglio Nazionale delle Ricerche, Rome.Acknowledgments. This work was performed with the technical assistence of the laboratory of Electron Microscopy of the University of Perugia.     

“Will someone say exactly what the H-theorem proves?” A study of Burbury's Condition A and Maxwell's Proposition II

Summary Many historians of science recognize that the outcome of the celebrated debate on Boltzmann's H-Theorem, which took place in the weekly scientific journal Nature, beginning at the end of 1894 and continuing throughout most of 1895, was the recognition of the statistical hypothesis in the proof of the theorem. This hypothesis is the Stosszahlansatz or hypothesis about the number of collisions. During the debate, the Stosszahlansatz was identified with another statistical hypothesis, which appeared in Proposition II of Maxwell's 1860 paper; Burbury called it Condition A. Later in the debate, Bryan gave a clear formulation of the Stosszahlansatz. However, the two hypotheses are prima facie different. Burbury interchanged them without justification or even warning his readers. This point deserves clarification, since it touches upon subtle questions related to the foundation of the theory of heat. A careful reading of the arguments presented by Burbury and Bryan in their various invocations of both hypotheses can clarify this technical point. The Stosszahlansatz can be understood in terms of geometrical invariances of the problem of a collision between two spheres. A byproduct of my analysis is a clarification of the debate itself, which is apparently obscure.     

Measuring unmet need for social care amongst older people

Recent spending cuts in the area of adult social care raise policy concerns about the proportion of older people whose need for social care is not being met. Such concerns are emphasised in the context of population ageing and other demographic changes. For example, the increasing proportion of the population aged 75 and over places greater pressure on formal and informal systems of care and support provision, while changes in the living arrangements of older people may affect the supply of informal care within the household. This article explores the concept of 'unmet need' for support in relation to specific Activities of Daily Living (ADLs) and Instrumental Activities of Daily Living (IADLs), using data on the receipt of support (informal, formal state or formal paid) from the General Household Survey, the English Longitudinal Study of Ageing and the British Household Panel Survey. The results show that different kinds of need tend to be supported by particular sources of care, and that there is a significant level of 'unmet need' for certain activities.     

Dislocation multi-junctions and strain hardening

At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects called dislocations. First proposed theoretically in 1934 (refs 1-3) to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening, a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions that tie the dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed 'multi-junctions'. We first predict the existence of multi-junctions using dislocation dynamics and atomistic simulations and then confirm their existence by transmission electron microscopy experiments in single-crystal molybdenum. In large-scale dislocation dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication, thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in body-centred cubic crystals.