Growth rate stimulation of marine pseudomonads by thiosulfate

The oxidation of thiosulfate to tetrathionate exerts a definite growth rate stimulation in glucose, acetate, and yeast extract cultures of some marine pseudomonads. The failure to find this effect in earlier studies with terrestrial isolates may lie in the particular conditions used in the present experiments (constant pH, high ratio of thiosulfate to organic substrate) or in the different metabolic characteristics of the marine isolates.Contribution No. 3220 from the Woods Hole Oceanographic Institution.     

Genetic Analysis of tox+ and tox? Bacteriophages of Corynebacterium diphtheriae

A series of mutants derived from the temperate corynebacteriophages beta(tox+), gamma(tox-), and L(tox+) was isolated and characterized. In three-factor crosses between mutant beta phages the relative map order of the genetic markers determining extended host ranges (h and h') and loss of ability to lysogenize (c) was found to be h--c--h'. Recombination between markers was observed in matings between phage beta and the heteroimmune corynebacteriophages gamma and L. In such matings between heteroimmune phages the c markers of phages beta and gamma failed to segregate from the imm markers which determine the specificity of lysogenic immunity in these phages. The factor which directs the synthesis of diphtherial toxin during infection of appropriate corynebacterial hosts by toxinogenic corynebacteriophages is designated tox(+). It was possible to show that the tox(+) determinant of phage beta behaves as a single genetic element which occupies a position between the loci h and imm on the genetic map of this phage. Genetic recombination between mutants of phage beta occurred at very low frequencies in biparental matings performed by mixed infection of Corynebacterium diphtheriae C7(s)(-)(tox-). Considerably higher recombination frequencies were observed when lysogenic bacterial strains carrying one parental phage as prophage were induced by ultraviolet irradiation and then superinfected by the second parental phage. Maximal stimulation of genetic recombination between mutant beta phages was detected when superinfection followed ultraviolet irradiation of the lysogenic cells within a limited period of time. In matings between phages with incomplete genetic homology, the stimulation of recombination by ultraviolet radiation was much less effective.     

The fine structure of the infundibular process of the hedgehog

Summary The fine structure of the infundibular process of the hedgehog has been studied, using material fixed in osmium tetroxide and embedded in Vestopal W. The process resembles in general structure that of other mammals, but also shows features not previously described in other species.The nerve fibres contain a number of inclusions, namely: small vesicles, 300–500 Å in diameter; larger vesicles, up to 2000 Å in diameter, which contain a variable amount of osmiophilic material; hexagonal crystal-like bodies, approximately 1250 × 3000 Å in size, lying within a striated membranous sheath; and aggregate bodies made up of small electron dense granules, possibly derived from mitochondria.In addition complex multilamellate bodies occur in some nerve fibres, which apparently give rise to membranous vesicles. Pituicytes, of varying appearance, are often intimately related to the nerve fibres.The findings suggest that synthesis of material may occur in the distal part of the fibres of the hypothalamo-hypophysial tract.We are indebted to the Medical Research Council, who provided the electron microscope in the Department of Anatomy, University of Birmingham, which was used in this study.     

The neurohypophysis of the foetal monkey

Summary The neurohypophysis of foetal macaque monkeys has been studied by optical and electron microscopy. Abundant elementary neurosecretory granules are present in the infundibular process by the middle third of gestation. Most of these are of variable electron density, and surrounded by a membrane larger than the granule, so that they appear haloed. A few fibres contain membrane-bounded electron-dense granules which show no halo. Inclusions of synaptic vesicle size are rare. The infundibular stem contains a few fibres with typical inclusions smaller than 1000 Å in diameter; the latter resemble inclusions in fibres of the median eminence.Dedicated to Professor W. Bargmann on his 60th birthday.     

Studies into equine electrocardiography and vectorcardiography: I. Cardiac electric forces and the dipole vector theory

Theoretical consideration has been given in two horses to the properties of the electric field created by the equine heart acting as a simple electric generator. The principles of the vectorial theory have been applied to test the validity of application of the dipole concept. The cardiac electric forces, althrough complex in the immediate region of the heart, appear at the body surface in a similar form to those arising from a relatively immobile, single equivalent dipole. The potential value of the technique of vectorcardiography in cardiological investigations is briefly discussed.     

Differential expression of the receptors for epidermal growth factor and insulin in the developing human placenta

The detailed cellular distribution of epidermal growth factor (EGF) receptors and insulin receptors during the development of the human placenta was examined. We show that EGF receptors are expressed by villous cytotrophoblast cells in first trimester human placentae. However, where these cells proliferate to form extravillous cytotrophoblast cell columns, there is a dramatic decrease in EGF receptor expression. There is no such differential expression of insulin receptors on this cell population. In contrast, both EGF-and insulin-receptors are present throughout gestation on the microvillous membrane of the terminally differentiated and non-proliferative syncytiotrophoblast although, at term, EGF-but not insulin-receptors are also found on the basolateral membrane of this epithelium. We further show that EGF receptors isolated from first trimester and term human placentae have functional tyrosine kinase activities but differ in their extent of glycosylation. These results suggest that EGF receptors probably play several distinct functional roles in these epithelial cells depending on their proliferative capacity and differentiation status.     

The nonlinear characteristics of soft gels and hydrated connective tissues in ultrafiltration

A one-dimensional ultrafiltration problem of fluid flow through a soft permeable tissue or gel under high pressure and compressive strain is solved. A finite deformation biphasic theory is used to model the behavior of the soft porous permeable solid matrix. This theory includes a Helmholtz free energy function which depends on the three principal invariants (I, II, III) of the right Cauchy-Green tensor and which satisfies the Baker-Ericksen inequalities on the principal stresses and strains. The dependence of the porosity phi f and the solidity phi s on deformation is deduced and a generalization of the exponential strain-dependent functional form for the permeability, k = k0 exp (M epsilon), of Lai and Mow (Biorheology 103, 111-123, 1980) is proposed. In this one-dimensional problem, we show that the dependence of the permeability on phi f, phi s, and III is equivalent to its dependence on hydration as proposed by Fatt and Goldstick (J. Colloid Sci. 20, 962-988, 1965). The exact solution of the ultrafiltration problem is derived and asymptotic and numerical methods are used to evaluate it. For high pressures and finite strains, the solution provides some surprising effects. The theory predicts that a material starting with a homogeneous porosity will have a strongly non-homogeneous porosity throughout the column during ultrafiltration. The resulting change in pore size through the filtration column may be very important in understanding its filtration characteristics. It is also found that there is a long delay time, up to 10 to 15 min, before the filtration velocity reaches an equilibrium. In filtration experiments where the rate of mass transport across the tissue or column of gel is important, sufficient time must be allowed for the steady state to be reached.