Abstract: Gardner and Ashby1 have suggested that large complex systems which are assembled (connected) at random may be expected to be stable up to a certain critical level of connectance, and then, as this increases, to suddenly become unstable. Their conclusions were based on the trend of computer studies of systems with 4, 7 and 10 variables.

Abstract: Chemotaxis toward amino-acids results from the suppression of directional changes which occur spontaneously in isotropic solutions.

Abstract: H2-receptor antagonist, a new group of drugs, may help to unravel the physiology of histamine and gastrin.

Abstract: Hydrogen may be compressed to more than 10,000 times liquid density by an implosion system energized by a high energy laser. This scheme makes possible efficient thermonuclear burn of small pellets of heavy hydrogen isotopes, and makes feasible fusion power reactors using practical lasers.

Abstract: The observed concatemers of T7 DNA are consistent with replication schemes resulting in double-helical molecules with 3´ ended tails. Right-ended and left-ended molecules can then join to form dimers which on further replication similarly form larger concatemers.

Abstract: THE classical theory of the resolving power of optical instruments implies a limit to the observation of details in an object if these are significantly smaller than one wavelength, λ0, of the illuminating radiation. This Abee barrier is not entirely impenetrable. Lukosz1,2 has shown how an improvement by a factor of two can be made by the use of complementary spatial filters. Attempts to proceed further in this direction are soon frustrated, however, because the spatial frequencies one is seeking to transfer are such that the waves become evanescent in the direction in which one would like them to propagate. Nassenstein has developed an ingenious scheme3 in which evanescent waves are used to illuminate the object, and a magnified image is obtained using a holographic technique. The resolution capability is determined by the wavelength of the evanescent wave. This is less than λ0, but it is not easy to devise systems where it would be very much smaller.

Abstract: THE importance of prostaglandins in inflammation has been emphasized by the discovery that aspirin-like anti-inflammatory drugs inhibit their synthesis1–3. The anti-inflammatory and anti-pyretic effects of this group of drugs could be explained on this basis1, but their analgesic properties could not, then, be firmly linked to inhibition of prostaglandin synthesis. This was because the only subjective effect reported on intradermal injection of prostaglandin was a sensation of warmth and a slight itching*, and on the blister base PGE2 (up to 100 µg/ml.) failed to produce pain5. Several reports now describe the pain-producing activity of prostaglandins infused i.v. and injected intramuscularly6–8 in man. Collier and Schneider have shown that PGE1 is the most powerful agent in producing writhing responses in mice9. Vane1 suggested that rabbit aorta contracting substance (RCS)10 which may be the unstable cyclic peroxide intermediate in the biosynthesis of prostaglandins11, may be involved in the production of pain in inflammation. I tried to test this hypothesis by comparing the pain producing activity of fatty acid hydroperoxides with that of high concentrations of acetylcholine, bradykinin, histamine and PGE1 on intradermal injection in man. The intensity of the pain induced by the hydroperoxides was greater than that induced by the other agonists but for all except PGE1 the pain was transitory. On testing subdermal infusions to mimic the continuous release of an endogenous mediator of pain, two important properties of E-type prostaglandins were revealed. First, they increase the pain sensitivity to chemical and mechanical stimulation. Second, their effects are cumulative and depend not only on their concentrations but also on the time of exposure. The term “pain” is used to denote the overt pain evoked chemically during the infusions; hyperalgesia is used when pain was elicited only by applying slight pressure on the infusion area. Studies were carried out in five male volunteers each of whom received a full explanation of the nature of the experiment before giving his consent. The experiments were double blind.

Abstract: INHIBITION of prostaglandin biosynthesis by aspirin-like drugs1–3 has now been confirmed in several systems4–7. The theory1 that this anti-enzyme action is the basis of the clinical effects of aspirin-like drugs has recently been reviewed8–11 in detail. One of the few anomalies was that paracetamol (4-acetamidophenol) which has no anti-inflammatory activity, but is analgesic and anti-pyretic12, was inactive against dog spleen synthetase (ED50 = 100 µg ml.−1). A possible explanation for this discrepancy is that synthetase systems from different regions of the body show different sensitivities to drugs.

Abstract: “Tight junctions” between cells in some epithelia actually provide the main route of passive ion permeation. The degree of junctional tightness may underlie important functional differences between different epithelia.

Abstract: Penrose1 and Christodoulou2 have shown how, in principle, rotational energy can be extracted from a black hole by orbiting and fissioning particles. Recently, Misner3 has pointed out that waves can also extract rotational energy (“superradiant scattering” in which an impinging wave is amplified as it scatters off a rotating hole). As one application of super-radiant scattering, Misner has suggested the possible existence of “floating orbits”, that is, orbits in which a particle radiatively extracts energy from the hole at the same rate as it radiates energy to infinity; thereby it experiences zero net radiation reaction.

Abstract: ALL models of natural processes for the transfer of sulphur on a global scale1–4 require some volatile or gaseous sulphur compound to complete the cycle by providing a vehicle for the transfer of sulphur from the sea through the air to the land surfaces. In the past, this role has been assigned to H2S and an average atmospheric concentration of 2×10−10 by volume satisfied the mass transfer needs of the models. Attempts to detect the presence of these concentrations of H2S have always failed and, more important, the ocean surface waters are much too oxidizing to permit the existence of H2S at concentrations sufficient to sustain an atmospheric equilibrium concentration of 2×10−10 by volume. Many elements form volatile methyl derivatives; Challenger5 reported that many living systems produced dimethyl sulphide (DMS), and that prominent among them were marine algae. Here we suggest that DMS is the natural sulphur compound which fills the role originally assigned to H2S; that of transferring sulphur from the seas through the air to land surfaces.

Abstract: IT is generally accepted that the matrix of cellular membranes is a bimolecular leaflet of phospholipid molecules in which the phospholipids are oriented so that their polar heads reside on the outer surfaces of the bilayer, in contact with the aqueous environment, the interior of the sandwich being composed of hydrophobic lipid chains1–5. To this basic structure proteins cholesterol, glycolipids and other molecules are usually inserted in such a way as to confer on the bilayer the functional properties appropriate for the particular membrane.

Abstract: This article summarizes Iranian geology and continental drift in the Middle East The relation of the two suggests that plate tectonics satisfactorily explain the geological development of the Middle East

Abstract: Simple rules are presented for rationalizing and predicting the geometries of complex polynuclear aggregates of atoms and molecular fragments

Abstract: WE have recently shown that the immune response to sheep red blood cells (SRBC) in vitro is T-cell dependent, that is, it can be abrogated by pretreatment of the spleen cells with anti-θ serum and complement1. We further reported that reconstitution of the system can be achieved by, among other things, the addition of allogeneic thymocytes2, while syngeneic thymocytes failed to function as helper cells. Positive allogeneic effects were only obtained if the added thymocytes could recognize the remaining B-cells as foreign. One of the explanations evoked for this allogeneic effect was the participation of a potentiating factor2,3. It seemed possible that on the heavy antigenic stimulation provided by the histocompatibility antigens carried by the B-cells, added T-cells produce a soluble factor which stimulates the immune response of B-cells to unrelated antigens. We now want to report the existence of two distinct factors, one of which can completely replace T-cells.

Abstract: To study new trace element deficiency diseases and to identify hitherto unrecognized essential trace elements, an all-plastic trace element controlled isolator system has been created1,2. It prevents access of the animals to metal, glass, rubber, dust, or caretaking personnel. Each isolator accommodates thirtytwo rats in individual plastic cages. Complete, chemically defined diets are used which are based on amino-acids in lieu of protein. The known essential elements are supplied in sufficient and balanced quantities. All ingredients are monitored for trace element contaminants. By means of this approach we have been able to demonstrate recently that tin3,4, vanadium5, and fluorine6 (K. S. and D. B. M., unpublished results) are essential for growth.

Abstract: By characterization of fragments, isolated from a nuclease digest of MS2 RNA, the entire nucleotide sequence of the coat gene was established. A “flower”-like model is proposed for the secondary structure. The genetic code makes use of 49 different codons to specify the sequence of the 129 amino-acids long coat polypeptide.

Abstract: MALARIA parasites1 or mammalian liver2 suitably exposed to chloroquine rapidly form autophagic vacuoles; in the case of the parasites, these are visible under the light microscope because they contain clumps of pigment, the remains of haemoglobin digestion (Fig. 1). These striking morphological changes are well known but not correspondingly well understood.

Abstract: Muscular movements are under the control of a servo similar in many ways to those used in engineering control systems but with a subtlety of design not found in man-made servo mechanisms—including an automatic gain compensation for altered load which must be useful, for example, for adjusting to reduced g on the Moon.

Abstract: A new computer simulation of random packing of spheres is applied to two- and three-dimensional problems with a uni-directional gravitational force.

Abstract: Comparison of the anti-inflammatory activities of several aspirin-like drugs with the inhibition of prostaglandin synthetase which they produce supports this as their mechanism of action.

Abstract: IN peripheral nerve, most axons with diameters of less than 1 µm do not have myelin sheaths, while most fibres more than 1 µm in diameter are myelinated1,2. In the central nervous system, axons as small as 0.2 µm in diameter may be myelinated2–5. In his paper on the effects of myelin on conduction velocity, Rushton6 concluded that 1 µm is the “critical diameter” above which “myelin increases conduction velocity” and below which “conduction is faster without myelination”. This conclusion is referred to widely (see, for example, refs. 7–9). In this communication we demonstrate that the analysis leading to this conclusion is based on morphological data10 which do not apply either to central or to peripheral fibres, so that myelinated fibres considerably smaller than 1 µm might be expected to conduct more rapidly than non-myelinated fibres of similar size.

Abstract: FLESHY fruits have been divided into two classes on the basis of their respiratory behaviour during ripening: climacteric fruit, such as bananas, which undergo a large increase in respiration (climacteric rise) accompanied by marked changes in composition and texture, and non-climacteric fruit such as citrus, which show no changes in respiration that can be associated with distinct changes in the composition of the fruit1. An increase in the level of endogenous ethylene is considered to be the immediate trigger of ripening in climacteric fruits2. Fruits of this class usually produce large amounts of ethylene once ripening is under way. They may also be induced to ripen by treatment with ethylene at concentrations above about 0.1 p.p.m. for a suitable period3. The ripening induced by exogenous ethylene has been considered to be qualitatively identical with that which occurs naturally3. In both cases, once ripening is induced it has been considered that endogenous ethylene production rises autocatalytically4. Uninjured citrus fruit have been shown to produce low amounts of ethylene5. Their respiration may be increased by treatment with ethylene6 and disappearance of chlorophyll (colouring) and ageing may be more rapid18.

Abstract: The three dimensional structure of human carbonic anhydrase C has been determined at 2.0 A resolution. The active site has been identified by the binding of inhibitors and the location of the zinc ion.

Abstract: Prostaglandin F2α is released from the uterus of the sheep in a cyclic fashion, acts primarily in a local manner on the ovary via a counter-current mechanism and is responsible for the periodic regression of the corpus luteum in this species.

Abstract: SYNTHESIS in the brain of the putative transmitter 5-hydroxytryptamine (5HT) is influenced by the concentration of tryptophan; the rate limiting step in 5HT synthesis is the hydroxylation of tryptophan1 by tryptophan hydroxylase, which is normally unsaturated with substrate2. Often when 5HT turnover in the rat brain increases—as indicated by higher concentrations of its metabolite 5-hydroxyindoleacetic acid (5HIAA)—there is a corresponding increase in brain tryptophan. This occurs when the rats are given various drugs known to increase brain 5HT synthesis3, deprived of food4,5, or immobilized5. Therefore the control of brain tryptophan concentration is clearly of some importance.

Abstract: TSUGE et al.1 have shown that β -Si3N4 can accommodate up to about 60% by weight Al2O3 in solid solution without major change of crystal structure but with increasing a and c unit-cell dimensions as the Al2O3 concentration increases. The products, obtained by sintering the mixed powders at 1,700 and 1,770° C, are undoubtedly similar to a new phase observed by Oyama and Kamigaito2 in mixtures of Si3N4, Al2O3 and Li2CO3 hot-pressed at 1,750° C. We report here a variety of ceramic materials built up of (Si,Al)(N,O)4 tetrahedra joined by sharing corners just as the silicate structures are built up of SiO4 and (Si,Al)O4 units.

Abstract: DAUNOMYCIN1–3, a glycosidic anthracycline antibiotic from Streptomyces peucetius4, is being used in the treatment of acute leukaemia and solid tumours in man5,6. The biological activity seems to be due to complex formation with the DNA of deoxyribonucleoprotein4. In vivo, daunomycin inhibits both RNA and DNA synthesis7,8 and, in vitro, DNA-dependent RNA polymerase and DNA polymerase7–9.