Showing papers by "University College London published in 1968"

Reasoning about a rule

Abstract: Two experiments were carried out to investigate the difficulty of making the contra-positive inference from conditional sentences of the form, “if P then Q.” This inference, that not-P follows from...

Inherited variations in human phosphohexose isomerase.

Abstract: SUMMARY 1. The elctrophoretic pattern of phosphohexose isomerase has been examine in the blood of 3397 unrelated individuals from several different populations groups. 2. Eight variant phenotypes were identinfied and these were designated PHI 2-1, 3-1, 4-1, 5-11 6-1, 7-1, 8-1, 9-1. All of these were rare in the populations studied except the variant designated PHI 3-1, which was observed with a frequency of about 1% in a mixed population of Asiatic Indians. 3. Studies of selected families indicated that the variants occured in individuals who are heterozygous for one or another of a series of rare alleles at an autosomal locus. 4. Studies on the family of a patient that the patient was heterozygous for two different rare alleles at the PHI locus, each associated with reduced PHI activity. The patinet's mother showed the PHI 9-1 phenotype and his father showed a new phenotype designated PHI 10-1. The patient's phenotype has been designeated PHI 9-10. 5. The enzyme appears to be a dimer and in heterozygotes isozymes of hybrid submit compostion as well as isozymes of like subunit compostion are apparently formed.

Changes of total water and sucrose space accompanying induced ion uptake or phosphate swelling of rat liver mitochondria

Abstract: 1. Total water exchangeable with tritiated water and sucrose space were measured in rat liver mitochondria during the uptake of K+ induced by valinomycin and the release caused by nigericin. The K+ content and the sucrose-inaccessible water rose and fell together. 2. Swelling resulting from phosphate addition in a medium of high K+ concentration was associated mainly with increased sucrose-accessible water, which carried dissolved K+. This change was reversed by addition of ATP. 3. The response of the sucrose-inaccessible space to changed osmolarity was qualitatively that expected if the mitochondrial K+ is assumed to be present in this space with a univalent anion. 4. It is brought out that the light-scattering method fails to distinguish between changes in sucrose space and in sucrose-inaccessible space, which in the present experiments could be altered respectively by phosphate (in high K+ solution) and by cation uptake induced by antibiotic.

Electrophysiology and electron-microscopy of rat neuromuscular junctions after nerve degeneration.

Abstract: (1) Intracellular micro-electrodes and electron-microscopy were used to study normal and denervated end-plates in rat diaphragm muscle fibres. (2) In normal muscles 84.5 to 100% of the micro-electrode insertions were sufficiently close to the neuromuscular junction to detect miniature end-plate potentials. The structure of the normal neuromuscular junction had the usual 3-cell arrangement: muscle with synaptic folds, axon and Schwann cell. (3) Within one day after section of the phrenic nerve, the axon disintegrated and miniature end-plate potentials ceased to occur. Subsequently, miniature potentials were not observed at denervated end-plates, except during the third week after denervation, at which time a low-frequency discharge was seen in eight out of 770 fibres. The miniature potentials at these end-plates resembled those at normal junctions, and were presumably also due to acetylcholine acting on the muscle membrane. (4) The synaptic folds remain for several months after denervation, and serve to identify electron-microscopically the denervated end-plate. After prolonged denervation (> 3 weeks), when miniature end-plate potentials were never observed, there was generally no cell overlying the synaptic folds. (5) During the first 3 weeks after denervation, a nucleated cell, presumably the Schwann cell, was in close contact with the muscle. 'Schwann-muscle' contacts were observed in muscle without miniature end-plate potentials. (6) Electron microscopy of a portion of denervated muscle, which included a fibre with miniature potentials, showed that the fibre had extensive 'Schwann-muscle' contacts. (7) It is concluded that the Schwann cell is the source of the packages of acetylcholine which evoke miniature end-plate potentials in denervated muscle. Since the Schwann cell was in contact with muscle fibres without miniature potentials, it appears that the presence of the Schwann cell is a necessary, but not a sufficient, condition for the production of miniature potentials at denervated end-plates.

Epitaxy as a growth factor in urinary calculi and gallstones.

Abstract: EPITAXY1 consists of the growth of one crystal, in one or more particular orientations, on a substrate of another, with a near geometrical fit between the respective networks which are in contact. Thus anthraquinone can grow on rocksalt2 and d- or l-camphor on d- or l-quartz3. That there is some influence of the structures themselves (apart from the geometry) has been proved, but it is of surprisingly minor importance3. There is also a dependence of the degree of misfit which can be tolerated on the degree of supersaturation of the solution from which the epitaxial crystals are deposited4.

Scanning electron microscopy of lamellar bone.

Abstract: Bone was prepared for scanning electron microscopy by sawing or fracturing into suitable pieces, most of which were extracted with hot 1, 2 ethane diamine to remove the organic matrix and cellular debris.

A Theoretical Treatment of the Reflexion of Light by Multilayer Structures

Abstract: 1. A convenient method is presented for calculating the reflectance of a stack of dielectric layers consisting of a series of identical repeats of any particular sequence of layers. The method is closely related to that published by Lord Rayleigh in 1917. 2. In this method, two quadratic equations are formed from the thicknesses and refractive indices of the layers composing a single repeat unit. The reflectance is obtained by substituting the solutions of these equations into an explicit formula. 3. Particularly simple formulae result for the case of a stack of p plates, optical thickness λo/2π, uniformly spaced in an infinite medium with spaces of the same optical thickness. If r is the amplitude reflexion coefficient at a single interface, the reflectance of the whole stack is as follows: ( a ) when cos 2 φ 2 , reflectance = 1/1+4m 2 (r 2 -cos 2 φ)/r 2 (1-m 2 ) 2 , where m=(1-√r 2 -cos 2 φ/sin 2 φ/1+√r 2 -cos 2 φ/sin 2 φ) p ; ( b ) when cos 2 φ > r 2 reflectance = 1/1+cos 2 φ-r 2 /r 2 sin 2 pθ, Where cosθ = cos2φ-r 2 /1-r 2 ; ( c )when the number of repeats in the stack is large ( p →∞), reflexion is complete so long as cos 2 φ 2 . Outside this range the reflections is 1-√(1-r 2 cos 2 φ). 4. These results are extended to cover: ( a ) unequal optical thicknesses in plates and spaces; ( b ) oblique incidence; ( c ) layers of materials of other refractive indices above and below the stack itself; and ( d ) stacks consisting of repeats of more complex units.

Salt Weathering in Deserts

Abstract: WEATHERING of rocks as the result of pressures exerted by the crystallization of salts from solutions in confined spaces has been recognized for many years. Studies of crystal growth pressures have been summarized by Buckley1. The roles of such pressures in rock weathering have been described by Birot2, and analysed by Wellman and Wilson3, who stated that for rocks of equal mechanical strength those with large pores separated from each other by microporous regions are most liable to salt weathering. The process is pronounced in desert and coastal areas. It is likely to be most effective (i) in the humid deserts of western littorals where the supply of salts from fogs and chemical weathering is accompanied by frequent wetting and drying of the surface, and (ii) around the margins of playas and along channels in desert areas where salts tend to be concentrated and wetting and drying is most frequent. We accept the effectiveness of salt crystallization pressures, the Salzsprengung of German authors, but we suggest that there are two additional factors associated with salts which may lead to the disintegration of rock: (i) stresses exerted by the expansion of many salts in confined spaces as they are heated, and (ii) stresses caused by hydration of certain salts in confined spaces.

Some changes in the reactivity of enzymes resulting from their chemical attachment to water-insoluble derivatives of cellulose

Abstract: 1. Purified ficin was chemically attached to CM-cellulose, and partially purified ATP–creatine phosphotransferase was chemically attached to both CM-cellulose and p-aminobenzylcellulose. 2. The apparent Km with respect to ATP and Mg2+ of ATP–creatine phosphotransferase was observed to increase about tenfold on attachment of the enzyme to CM-cellulose, and to increase by only 23% on its attachment to p-aminobenzylcellulose. 3. The reactivity of both ficin and ATP–creatine phosphotransferase with 5,5′-dithiobis-(2-nitrobenzoic acid) was observed to decrease on chemical attachment of these enzymes to water-insoluble derivatives of cellulose. With derivatives prepared from CM-cellulose, the extent of the reaction with 5,5′-dithiobis-(2-nitrobenzoic acid) was dependent on ionic strength, but with similar derivatives prepared from p-aminobenzylcellulose the extent of this reaction was independent of ionic strength. 4. The effect of diffusion and electrostatic interaction of charged enzyme substrates and charged enzyme supports on the apparent Km of a water-insoluble derivative of an enzyme is discussed. An equation is derived that satisfactorily describes the observed effects of these factors on the apparent Km.

The dorsal root distribution to the substantia gelatinosa of the rat with a note on the distribution in the cat.

Abstract: The terminal degeneration in the substantia gelatinosa of the rat was studied with the Fink-Heimer silver technique following dorsal root section. Providing the survival time of the animal was in the range of 1–4 days, a massive degeneration was seen in lamina I, II and III of Rexed. The light microscope findings were corroborated by electronmicroscopic observations of degenerating boutons. Spinal cord material examined with silver methods one week after dorsal root section showed few signs of degeneration in the substantia gelatinosa. Although a significant dorsal root distribution to the substantia gelatinosa was found also in the cat, the terminal degeneration in lamina II showed considerable regional variations in this species.

A third phosphoglucomutase locus in man.

Abstract: SUMMARY 1. Investigation of human tissue extracts by starch gel electrophoresis has vevealed three groups of isozymes with PGM activity. 2. Previous studies on red cell lysates have established that two of these groups of isozymes, PGM1 and PGM2 are determined by two separate autosomal loci, PGM1 and PGM2 respectively. 3. The new series of isozymes, designated PGM3, are electrophoretically faster than the other PGM components, constitute only a small fraction of the total PGM activity, and exhibit person-to-person differences in electrophoretic patten which are independent of te PGM1 and PGM2 variants. Three commonly occuring phenotypes have been recognized : PGM3 1, PGM3 2-1 and PGM3 2. 4. The genetics of this polymorphism have been studied using plancentae derived from pairs of non-identical twins. The reult suggest the occurence of two common alleles PGM1/3 and PGM2/3 at an atosomal locus, with frequencies of 0.74 and 0.26 respectively in the English population and 0.34 and 0.66 respectively in the Nigerian population. 5. Tests for linkage using the twin data indicate that the PGM1 and PGM3 loci are not closely linked. 6. The possibility of structural homologies between the various PGM isozymes is noted.

The derivation and application of the bradford‐zipf distribution

Abstract: Any statistical regularities found in documentation should be fully exploited to produce estimates or predictions and to save documentalists work. But present formulations of the Bradford distribution demand penetrating search for peripheral papers and tedious computation in application. The present paper shows that the Bradford distribution is closely related to the Zipf distribution. It requires data on only the most productive journals, is mathematically simple and amenable to graphical methods if a proposed idea of the ‘completeness’ of a search is accepted. For comparability of results, certain conditions, which include a specified minimum level of productivity of journals, need to be standardized. A standard form is suggested. It is found, however, that a modified form of the Bradford distribution is required when Bradford‐type collections of journals are merged into larger collections, when ‘saturation’ of the most productive journals occurs.

Human Stones: Limited studies give some details of composition, rates of growth, distribution, and possible causes

Abstract: X-ray diffraction studies have shown that there are several different kinds of human urinary calculi, with different age, sex, period, and geographical distributions. Juvenile bladder stones are typically urate and oxalate in small boys in certain stone belts. They have disappeared in some areas, particularly in Britain, but are still common in Thailand. India. and Turkey. Their cause is unknown. Adult bladder stones, formerly common in elderly men, were largely of uric acid and were due to a faulty diet. Juvenile kidney stones are rare, except in Turkey where they are similar to juvenile bladder stones. Adult kidney stones are by far the most universally common, especially in technically developed communities. They are found in both sexes (equally at postmortem), and in the United States and in Czechoslovakia the average number of hospital entries for stones, relative to the whole population, is about 1 per 1000 per annum (increasing) although the incidence in different districts varies by 4 to 1 or more. Such stones are mainly calcium oxalates and calcium and MgNH4 phosphates. The incidence among the administrative class is at least 20 times that among agricultural workers, relative to their numbers. Stones are reported also to be an occupational hazard for air pilots. It is probably that much more exercise and the drinking of more water to prevent kidney dehydration (spirits and coffee are not effective for this purpose) would lower the high rate of incidence. Moderate acidification would prevent phosphate supersaturation of the urine, but is not effective for oxalates. It seems certain that, once a suitable seed is formed, epitaxy is largely responsible for deposition from urines that would otherwise remain supersaturated until voided. This would explain the curioLls radial and layered texture of many stones. Laboratory experiments might suggest ways of preventing orientated overgrowth.

Inhibition of mitochondrial synthesis in yeast by erythromycin: cytoplasmic and nuclear factors controlling resistance

Abstract: Erythromycin-resistant mutants were separated into two categories showing Mendelian and non-Mendelian inheritance of resistance respectively. The cytoplasmic factor was located in the mitochondrion based on the fact that the loss of the mitochondrial genetic unit associated with the petite mutation (the ρ factor, assumed to be the mitochondrial DNA) resulted in a corresponding permanent loss of resistance. Conversely, the petite mutation in gene resistant mutants had no effect on the inheritance of resistance.Analysis of vegetative and sexual progeny of isolated zygotes from a number of crosses between resistant and sensitive strains indicated that different mitochondrial types, both sensitive and resistant, co-exist in the yeast cell and are distributed at random among daughter cells under non-selective conditions. Only resistant mitochondria are in evidence if zygotes are put down to proliferate on medium containing the antibiotic.Resistant strains were tested for retention of resistance following anaerobic culture (known to cause disruption of mitochondria). The cytoplasmic mutants retained their resistance but two gene-resistant mutants tested both lost their resistance. It was suggested in the latter case that resistance is dependent on the existence of intact mitochondrial membrane (possibly inner membrane). In the former mutants the mechanism of resistance may be the alteration of one or other of the components of the protein-synthesizing system of the organelle.

Data on the incidence, segregation and linkage relations of the adenylate kinase (AK) polymorphism.

Abstract: Genetically determined variation in the enzyme adenylate kinase (AK) hm been described by Fildes 6 Harris (1966). About 90 yo of the English population were found to have an electrophoretic pattern designated AK 1, whilst 10 % had a different pattern, AK 2-1. Family studies showed that these phenotypes are determined by two autosomal alleles, AK1 and AK2, phenotype AK l corresponding to genotype AKlAKl and phenotype AK 2-1 to AK1AK2. The third phenotype, corresponding to the genotype AK2AK2, is relatively rare but has been observed both in the general population and in the offspring of AK 2-1 x 2-1 matings. These results have been confirmed by Bowman et al. (1967), who also described two unrelated examples of another phenotype referred to as AK 3-1. No family studies were performed in these cases. They also showed that in Negro populations the AK2 allele is very infrequent. In the present paper we shall give an analysis of routine AK typing on red cells from over 3000 individuals and of studies on 127 unselected families where one or both parents were of type AK 2-1.

Regulation of methionine synthesis in Salmonella typhimurium: mutants resistant to inhibition by analogues of methionine

Abstract: BIOCHEMICAL and genetical experiments with methionine auxothrophs of Salmonella typhimurium (SMITH 1961 ; SMITH and CHILDS 1966; CHILDS and SMITH unpublished) have resulted in the recognition of six structural genes ( m t A , B, C, E, F and H ) concerned with well defined sequential steps in the biosynthesis of methionine (Figure 1) . Mutants of another gene (metG) do not have a specific enzyme deficiency: they are leaky due to a low level of activity of all the methimine enzymes. Methionine inhibits the activity of homoserine O-transsuccinylase (metA) and represses the synthesis of all the enzymes of the pathway (ROWBURY 1964). Two pairs of genes (metA and H and metB and F ) are linked closely enough to be co-transducible whereas the mete, E and G genes are each located in well separated regions of the circular bacterial genome (Figure 3). On the basis of this partial clustering of genes concerned with related functions, it seemed likely that the mode of regulation of methionine synthesis in this organism would be sufficiently different from that of the control of lactose (BECKWITH 1967) and arabinose fermentation (ENGLESBERG et al. 1965) in EScherichia coli, histidine (AMES et al. 1967) and leucine (BURNS et al. 1966) synthesis in S. typhimurium and tryptophan synthesis in both organisms (BLUME and BALBINDER 1966; YANOFSKY and LENNOX 1959) to justify further investigation. Mutants of bacteria resistant to inhibition by analogues of metabolic end products have often been shown to be abnormal in regulation of the biosynthesis of the normal end product ( COHEN and JACOB 1959) and to be readily amenable to both biochemical and genetic analyses. The methionine analogues a-DL-methyl methionine, DL-ethionine and DL-norleucine were found to be inhibitory and this paper is concerned with the isolation, phenotypic characterisation, enzymic abnormalities and mapping of mutants resistant to these analogues. Preliminary results (SMITH and LAWRENCE 1966) suggested that the regulation of methionine synthesis in S . typhimurium possesses some unique features.

Theories of Scientific Method from Plato to Mach: A Bibliographical Review

Abstract: MUCH pious lip-service has been paid to the idea that the history of science and the philosophy of science are integrally dependent on one another. Yet the marriage between the two disciplines, sanctioned and perpetuated by the existence of dozens of academic departments of the subject, often seems more fanciful than real and more contrived than natural. University departments and chairs with hybridised names are, in themselves, obviously not sufficient to demonstrate any real affinity between the two subjects. Moreover, in actual practice, the two are often quite irrelevant to one another. For instance, it is difficult to imagine how the historian writing about the evolution of valency theory or science in revolutionary France will profit more from studying the philosophy of science than, say, political history or sociology. Similarly, the philosopher of science concerned about the paradoxes of confirmation or the existential status of theoretical entities is unlikely to gain much enlightenment from a prolonged exposure to the history of alchemy or systematic botany. But if the case for general interdependence between the history and philosophy of science is less convincing than some of its proponents are willing to admit, there is an excellent case for a slightly weaker interdependence claim. Rather than adopting the thesis that historical studies in general will aid the philosopher of science and vice versa, I think we should be stressing that both the history and philosophy of science have a common concern about, and vested interest in, one particular subject-the history of theories of scientific method. Indeed, it is difficult to understand either the history or the philosophy of sciencewithout dealing with the evolution of theories of method. Thus, the historian of science must deal with this issue continually because the views of

The preparation and kinetics of lactate dehydrogenase attached to water-insoluble particles and sheets.

Abstract: 1. The preparation of lactate dehydrogenase covalently attached to anion-exchange cellulose particles and sheets by use of a dichloro-sym-triazinyl dyestuff, Procion brilliant orange MGS, is described. 2. The stability and kinetic properties of these preparations were investigated. 3. An equation is derived to describe the change in concentration of a substrate when passed through a uniform bed of a substrate-inhibited enzyme. A number of theoretical curves are shown to illustrate the system. 4. A titrimetric assay for lactate dehydrogenase is described, and shown to be stoicheiometric over the range pH5·0–9·2. 5. The results are discussed in relation to previous work, and the effects of charged groups on the support, and of the diffusion film surrounding any particle in suspension, are treated qualitatively.