Showing papers in "Science in 1971"
TL;DR: The time required to recognize that two perspective drawings portray objects of the same three-dimensional shape is found to be a linearly increasing function of the angular difference in the portrayed orientations of the two objects.
Abstract: The time required to recognize that two perspective drawings portray objects of the same three-dimensional shape is found to be (i) a linearly increasing function of the angular difference in the portrayed orientations of the two objects and (ii) no shorter for differences corresponding simply to a rigid rotation of one of the two-dimensional drawings in its own picture plane than for differences corresponding to a rotation of the three-dimensional object in depth.
5,331 citations
TL;DR: In this paper, the authors argue that population growth causes a disproportionate negative impact on the environment and that the control of population is necessary but not sufficient means of seeing us through the whole crisis of environmental deterioration.
Abstract: There have been some questionable assertions relating to population growth. The most serious of these is the notion that the size and growth rate of the U.S. population are only minor contributors to this countrys adverse impact on local and global environment. The discussion in this article centers around 5 theorems which demonstrate the following: 1) population growth causes a disproportionate negative impact on the environment 2) the control of population is necessary but not sufficient means of seeing us through the whole crisis of environmental deterioration 3) population density is a poor measure of population pressure 4) environment as a term must be broadly construed to include physical environment of urban ghettos as well as the human behavioral environment and 5) theoratical solutions to out problems are not operational and some times are not solutions. The paper concludes that population control the redirection of technology the transition from open to closed resouce cycles the equitable distribution of opportunity and the ingredients of prosperity must all be accomplished if there is to be a future worth living.
2,381 citations
TL;DR: Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test, interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory.
Abstract: Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test. Most cells increase firing during the cue presentation period or at the beginning of the ensuing delay; spike discharge highler than that in intertrial periods is present in some cells throughout the delay. These changes are interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory
1,838 citations
TL;DR: Removal of phosphate from detergents is not likely to slow the eutrophication of coastal marine waters, and its replacement with nitrogen-containing nitrilotriacetic acid may worsen the situation.
Abstract: The distribution of inorganic nitrogen and phosphorus and bioassay experiments both show that nitrogen is the critical limiting factor to algal growth and eutrophication in coastal marine waters. About twice the amount of phosphate as can be used by the algae is normally present. This surplus results from the low nitrogen to phosphorus ratio in terrigenous contributions, including human waste, and from the fact that phosphorus regenerates more quickly than ammonia from decomposing organic matter. Removal of phosphate from detergents is therefore not likely to slow the eutrophication of coastal marine waters, and its replacement with nitrogen-containing nitrilotriacetic acid may worsen the situation.
1,828 citations
TL;DR: Recovery from habituation was greater for a given acoustic difference when the two stimuli were from different adult phonemic categories than when they were from the same category.
Abstract: Discriminiationi of synthetic speech sounds was studied in 1- and 4-month-old infants. The speech sounds varied along an acoustic dimension previously shown to cue phonemic distinctions among the voiced and voiceless stop consonants in adults. Discriminability was measured by an increase in conditioned response rate to a second speech sound after habituation to the first speech sound. Recovery from habituation was greater for a given acoustic difference when the two stimuli were from different adult phonemic categories than when they were from the same category. The discontinuity in discrimination at the region of the adult phonemic boundary was taken as evidence for categorical perception.
1,791 citations
TL;DR: Man must be very careful in attempting to enrich an ecosystem in order to increase its food yield, because there is a real chance that such activity may result in decimation of the food species that are wanted in greater abundance.
Abstract: Six reasonable models of trophic exploitation in a two-species ecosystem whose exploiters compete only by depleting each other's resource supply are presented. In each case, increasing the supply of limiting nutrients or energy tends to destroy the steady state. Thus man must be very careful in attempting to enrich an ecosystem in order to increase its food yield. There is a real chance that such activity may result in decimation of the food species that are wanted in greater abundance.
1,767 citations
TL;DR: The quadratic elongation is dimensionless, giving a quantitative measure of polyhedral disortion which is independent of the effective size of the polyhedron.
Abstract: Quadratic elongation and the variance of bond angles are linearly correlated for distorted octahedral and tetrachedral corrdination complexes, both of which show variations in bond length and bond angle. The quadratic elongation is dimensionless, giving a quantitative measure of polyhedral disortion which is independent of the effective size of the polyhedron.
1,671 citations
TL;DR: The overall conclusion is that a broad spectrum of cellular and developmental processes are caused by contractile apparatuses that have at least the common feature of being sensitive to cytochalasin.
Abstract: In our opinion, all of the phenomena that are inhibited by cytochalasin can be thought of as resulting from contractile activity of cellular organelles. Smooth muscle contraction, clot retraction, beat of heart cells, and shortening of the tadpole tail are all cases in which no argument of substance for alternative causes can be offered. The morphogenetic processes in epithelia, contractile ring function during cytokinesis, migration of cells on a substratum, and streaming in plant cells can be explained most simply on the basis of contractility being the causal event in each process. The many similarities between the latter cases and the former ones in which contraction is certain argue for that conclusion. For instance, platelets probably contract, possess a microfilament network, and behave like undulating membrane organelles. Migrating cells possess undulating membranes and contain a similar network. It is very likely, therefore, that their network is also contractile. In all of the cases that have been examined so far, microfilaments of some type are observed in the cells; furthermore, those filaments are at points where contractility could cause the respective phenomenon. The correlations from the cytochalasin experiments greatly strengthen the case; microfilaments are present in control and "recovered" cells and respective biological phenomena take place in such cells; microfilaments are absent or altered in treated cells and the phenomena do not occur. The evidence seems overwhelming that microfilaments are the contractile machinery of nonmuscle cells. The argument is further strengthened if we reconsider the list of processes insensitive to cytochalasin (Table 2). Microtubules and their sidearms, plasma membrane, or synthetic machinery of cells are presumed to be responsible for such processes, and colchicine, membrane-active drugs, or inhibitors of protein synthesis are effective at inhibiting the respective phenomena. These chemical agents would not necessarily be expected to affect contractile apparatuses over short periods of time, they either do not or only secondarily interfere with the processes sensitive to cytochalasin (Table 1). It is particularly noteworthy in this context that microtubules are classed as being insensitive to cytochalasin and so are not considered as members of the "contractile microfilament" family. The overall conclusion is that a broad spectrum of cellular and developmental processes are caused by contractile apparatuses that have at least the common feature of being sensitive to cytochalasin. Schroeder's important insight (3) has, then, led to the use of cytochalasin as a diagnostic tool for such contracile activity: the prediction is that sensitivity to the drug implies presence of some type of contractile microfilament system. Only further work will define the limits of confidence to be placed upon such diagnoses. The basis of contraction in microfilament systems is still hypothetical. Contraction of glycerol-extracted cells in response to adenosine triphosphate (53), extraction of actin-like or actomyosin-like proteins from cells other than muscle cells (54), and identification of activity resembling that of the actomyosin-adenosine triphosphatase system in a variety of nonmuscle tissues (40, 54) are consistent with the idea that portions of the complex, striated muscle contractile system may be present in more primitive contractile machinery. In the case of the egg cortex, calcium-activated contractions can be inhibited by cytochalasin. If, as seems likely, microfilaments are the agents activated by calcium, then it will be clear that they have the same calcium requirement as muscle. Biochemical analyses of primitive contractile systems are difficult to interpret. Ishikawa's important observation (31), that heavy meromyosin complexes with fine filaments oriented parallel to the surface of chondrocytes and perpendicular to the surface of intestinal epithelial cells, implies that both types of filaments are "actin-like" in this one respect. Yet, it is very likely that these actin-like filaments correspond respectively to the cytochalasin-insensitive sheath of glial and heart fibroblasts and the core filaments of oviduct microvilli. No evidence from our studies links contractility directly to these meromyosin-binding filaments. Apart from this problem, activity resembling that of the myosin-adenosine triphosphatase has been associated with the microtubule systems of sperm tails and cilia (55), but those organelles are insensitive to cytochalasin in structure and function. Clearly, a means must be found to distinguish between enzymatic activities associated with microfilament networks, microfilament bundles, microtubules, and the sheath filaments of migratory cells. Until such distinctions are possible, little of substance can be said about the molecular bases of primitive contractile systems. Three variables are important for the control of cellular processes dependent upon microfilaments: (i) which cells of a population shall manufacture and assemble the filaments; (ii) where filaments shall be assembled in cells; and (iii) when contractility shall occur. With respect to distribution among cells, the networks involved in cell locomotion are presumed to be present in all cells that have the potential to move in cell culture. In this respect, the networks can be regarded as a common cellular organelle in the sense that cytoplasmic microtubules are so regarded. In some developing systems, all cells of an epithelium possess microfilament bundles (7, 13), whereas, in others, only discrete subpopulations possess the bundles (5, 6). In these cases the filaments can be regarded as being differentiation products associated only with certain cell types. These considerations may be related to the fact that microfilament networks are associated with behavior of individual cells (such as migration, wound healing, and cytokinesis), whereas the bundles are present in cells that participate in coordinated changes in shape of cell populations. With respect to placement in cells, two alternatives are apparent, namely, localized or ubiquitous association with the plasma membrane. Microfilament bundles of epithelial cells are only found extending across the luminal and basal ends of cells. In this respect they contrast with desmosomal tonofilaments and with microtubules, each of which can curve in a variety of directions through the cell. The strict localization of microfilament bundles probably rests upon their association with special junctional complex insertion regions that are only located near the ends of cells. In the case of mitotically active cells, the orientation of the spindle apparatus may determine the site at which the contractile ring of microfilaments will form (4, 56); this raises the question of what sorts of cytoplasmic factors can influence the process of association between filament systems and plasma membranes. In contrast to such cases of localized distribution, contractile networks responsible for cell locomotion are probably found beneath all of the plasma membrane, just as the network of thrombosthenin may extend to all portions of the periphery of a blood platelet. This ubiquitous distribution probably accounts for the ability of a fibroblast or glial cell to establish an undulating membrane at any point on its edge, or of an axon to form lateral microspikes along its length. The third crucial aspect of control of these contractile apparatuses involves the choice of when contraction shall occur (and as a corollary the degree or strength of contraction that will occur). In the simplest situation, contraction would follow automatically upon assembly of the microfilament bundles or networks. In cleavage furrows of marine embryos (4), for instance, microfilaments are seen beneath the central cleavage furrow and at its ends, but not beyond, under the portion of plasma membrane that will subsequently become part of the furrow. This implies that the furrow forms very soon after the contractile filaments are assembled in the egg cortex. In other cases, microfilaments are apparently assembled but not in a state of (maximal?) contraction. Thus, networks are seen along the sides of migratory cells, although such regions are not then active as undulating membrane organelles. Similarly, microfilament bundles occur in all epithelial cells of the salivary gland (13), or pancreatic anlage (7), although only the ones at discrete points are thought to generate morphogenetic tissue movements. Likewise, bundles begin to appear as early as 12 hours after estrogen administration to oviduct, although visible tubular gland formation does not start until 24 to 30 hours. Finally, streaming in plant cells can wax and wane, depending upon external factors such as auxin (57). All of these cases imply a control mechanism other than mere assembly of the microfilament systems and even raise the possibility that within one cell some filaments may be contracting while others are not. In discussing this problem, it must be emphasized that different degrees of contraction or relaxation cannot as yet be recognized with the electron microscope. In fact, every one of the cases cited above could be explained by contraction following immediately upon some subtle sort of "assembly." Inclusive in the latter term are relations between individual filaments, relations of the filaments and their insertion points on plasma membrane, and quantitative alterations in filament systems. Furthermore, the critical role of calcium and high-energy compounds in muscle contraction suggest that equivalent factors may be part of primitive, cytochalasinsensitive systems. The finding that calcium-induced contraction in the cortex of eggs is sensitive to cytochalasin strengthens that supposition and emphasizes the importance of compartmentalization of cofactors as a means of controlling microfilaments in cells.
1,457 citations
TL;DR: Spin echo nuclear magnetic resonance measurements may be used as a method for discriminating between malignant tumors and normal tissue and Spin-lattice relaxation times for two benign fibroadenomas were distinct from those for both malignant tissues and were the same as those of muscle.
Abstract: Spin echo nuclear magnetic resonance measurements may be used as a method for discriminating between malignant tumors and normal tissue. Measurements of spin-lattice (T 1 ) and spin-spin (T 2 ) magnetic relaxation times were made in six normal tissues in the rat (muscle, kidney, stomach, intestine, brain, and liver) and in two malignant solid tumors, Walker sarcoma and Novikoff hepatoma. Relaxation times for the two malignant tumors were distinctly outside the range of values for the normal tissues studied, an indication that the malignant tissues were characterized by an increase in the motional freedom of tissue water molecules. The possibility of using magnetic relaxation methods for rapid discrimination between benign and malignant surgical specimens has also been considered. Spin-lattice relaxation times for two benign fibroadenomas were distinct from those for both malignant tissues and were the same as those of muscle.
1,354 citations
TL;DR: The existence of alliesthesia implies the presence of internal signals modifying the concious sensations aroused from peripheral receptors, and it is necessary to question the existence of sensations aroused by direct stimulation of central receptors, such as hypothalamic temperature detectors, osmoreceptors, and others.
Abstract: A given stimulus can induce a pleasant or unpleasant sensation depending on the subject's internal state. The word alliesthesia is proposed to describe this phenomenon. It is, in itself, an adequate motivation for behavior such as food intake or thermoregulation. Therefore, negative regulatory feedback systems, based upon oropharingeal or cutaneous thermal signals are peripheral only in appearance, since the motivational component of the sensation is of internal origin. The internal signals seem to be complex and related to the set points of some regulated variables of the "milieu interieur," like set internal temperature in the case of thermal sensation (15). Alliesthesia can therefore explain the adaptation of these behaviors to their goals. Only three sensations have been studied- thermal, gustatory, and olfactory, but it is probable that alliesthesia also exists in such simple ways as in bringing a signal, usually ignored, to the subject's attention. For example, gastric contractions, not normally perceived, are felt in the state of hunger (16). Since alliesthesia relies on an internal input, it is possible that alliesthesia exists only with sensations related to some constants of the "milieu interieur" and therefore would not exist in visual or auditory sensations. As a matter of fact, luminous or auditory stimuli can be pleasing or displeasing in themselves, but there seems to be little variation of pleasure in these sensations, that is, no alliesthesia. There may be some esthetic value linked to these stimuli but it is a striking coincidence that they are in themselves rather neutral and that it is difficult to imagine a constant of the "milieu interieur" which could be possibly modified by a visual or an auditive stimulus-such as light of a certain wavelength or sound of a given frequency. In the light of this theory, it is possible to reconsider the nature of the whole conscious experience. The existence of alliesthesia implies the presence of internal signals modifying the concious sensations aroused from peripheral receptors. It is therefore necessary to question the existence of sensations aroused by direct stimulation of central receptors, such as hypothalamic temperature detectors, osmoreceptors, and others. Does their excitation arouse sensations of their own, or does the sensation have to pass through peripheral senses? Only human experimentation could answer this question. In the same way, it is possible that selfstimulation of the brain is pleasant, not by giving a sensation in itself, but because the electrical stimulus (17), renders peripheral stimuli pleasant.
1,331 citations
TL;DR: Brain serotonin cocentrations at 1 p.m. were significantly elevated 1 hour after rats received a dose of L-tryptophan and plasma and brain tryptophan levels were elevated 10 to 60 minutes after the injection, but they never exceeded the concentrationis that occur nocturnally in untreated aninmals as result of their normal 24-hour rhythms.
Abstract: Brain serotonin cocentrations at 1 p.m. were significantly elevated 1 hour after rats received a dose of L-tryptophan (12.5 milligrams per kilogram. intraperitoneally) smaller than one-twentieth of the normal daily dietary intake. Plasma and brain tryptophan levels were elevated 10 to 60 minutes after the injection, but they never exceeded the concentrationis that occur nocturnally in untreated aninmals as result of their normal 24-hour rhythms. These data suggest that physiological changes in plasma tryptophan concentration influenice brain serotonin levels.
TL;DR: A radical chain reaction is proposed for the rapid removal of carbon monoxide, leading to acarbon monoxide lifetime as low as 0.2 year in the surface atmosphere.
Abstract: A steady-state model of the normal (unpolluted) surface atmosphere predicts a daytime concentration of hydroxyl, hydroperoxyl, and methylperoxyl radicals approaching 5 x 10(8)molecules per cubic centimeter and a formaldehyde concentration of 5 x 10(10) molecules per cubic centimeter or 2 parts per billion. A radical chain reaction is proposed for the rapid removal of carbon monoxide, leading to a carbon monoxide lifetime as low as 0.2 year in the surface atmosphere.
TL;DR: It seems that cholinergic synapses are modified as a result of learning and that it probably is the postsynaptic membrane that becomes increasingly more sensitive to acetylcholine with time after learning, up to a certain point.
Abstract: The idea that learning and memory are due to some form of change of synaptic conductance is very old, having been suggested by Tanzi in 1893. It is a simple idea and in many ways an obvious one. However, the evidence that learning is due to changes at the synapse has hitherto been meager (Eccles, 1961, 1964; Spencer and Wigdor, 1965; Beswick and Conroy, 1965; Fentress and Doty, 1966). Though changes do occur at a spinal synapse as a result of stimulation, there is no evidence that the changes are those utilized in the nervous system for information storage. To use an analogy, if we pass large amounts of current across resistors in a computer, temporary increases in temperature and perhaps even permanent increases in resistance occur. However, such an experiment shows only that the computer could store information by using “post-stimulation” alterations in its resistors but not that this is the actual way in which the computer does store information. Further, Sharpless (1964) has pointed out that learning is not due to simple use of stimulation of a pathway and he therefore questions whether the phenomena studied by Eccles (1961, 1964) have anything to do with learning as observed in the intact organism. Nevertheless this does not mean that learning is not due to synaptic changes of some sort. It means only that a different experimental test of the possibility must be devised.
TL;DR: The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.
Abstract: Although a great deal of attention has been given to the role of water vapor from supersonic transport (SST) exhaust in the stratosphere, oxides of nitrogen from SST exhaust pose a much greater threat to the ozone shield than does an increase in water. The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.
TL;DR: The early-stage annual rings in otoliths from some cold-temperate fish consist of thin growth bands, the number of which corresponds to that of the days in a year, which indicates that growth takes place by daily increments.
Abstract: The early-stage annual rings in otoliths from some cold-temperate fish consist of thin growth bands, the number of which corresponds to that of the days in a year. This indicates that growth takes place by daily increments. Other recurrent patterns show a fortnightly and monthly periodicity. Spawning rings are microscopically distinguishable from winter rings.
TL;DR: The correlation among a variety of physiological properties and the histochemical characteristics of muscle fibers belonging to single motor units in a mixed mammalian muscle is directly demonstrated.
Abstract: The correlation among a variety of physiological properties and the histochemical characteristics of muscle fibers belonging to single motor units in a mixed mammalian muscle is directly demonstrated. The population of motor units making up the cat gastrocnemius was classified into three nonoverlapping groups on the basis of a combination of physiological parameters. The muscle fibers belonging to motor units of each physiological type exhibited a distinctive histochemical profile, such that the three basic histochemical "fiber types" exactly matched the three physiologically defined groups. Within each individual motor unit, the muscle fibers were histochemically uniform.
TL;DR: Application and extension of Ogston's (random fiber) model for a gel allows for calculation of molecular volume, surface area, or radius, free mobility, and valence from RJ measurements at several gel concentrations, and to predict behavior of macromolecules on gel gradients by computerized methods.
Abstract: Polyacrylamide gel electrophoresis (PAGE) provides a versatile, gentle, high resolution method for fractionation and physical-chemical characterization of molecules on the basis of size, conformation, and net charge. The polymerization reaction can be rigorously controlled to provide uniform gels of reproducible, measurable pore size over a wide range. This makes it possible to obtain reproducible relative mobility (Rf) values as physical-chemical constants. Application and extension of Ogston9s (random fiber) model for a gel allows for calculation of molecular volume, surface area, or radius, free mobility, and valence from RJ measurements at several gel concentrations, to calculate gel concentration for optimal resolution, and to predict behavior of macromolecules on gel gradients by computerized methods. Extension of classical moving boundary theory has been used to generate multiphasic buffer systems (providing selective stacking, unstacking, restacking, and preparative steady-state-stacking) with known operating characteristics for any pH at 0° and 25°C. A general strategy for isolation of macromolecules and for macromolecular mapping has been developed. Preparative scale PAGE is operational for milligram loads and feasible for gram quantities.
TL;DR: Stimulation at several mesencephalic and diencephalic sites abolished responsiveness to intense pain in rats while leaving responsiveness to other sensory modes relatively unaffected.
Abstract: Stimulation at several mesencephalic and diencephalic sites abolished responsiveness to intense pain in rats while leaving responsiveness to other sensory modes relatively unaffected. The peripheral field of analgesia was usually restricted to one-half or to one quadrant of the body, and painful stimuli applied outside this field elicited a normal reaction. Analgesia outlasted stimulation by up to 5 minutes. Most electrode placements that produced analgesia also supported self-stimulation. One placement supported self-stimulation only in the presence of pain.
TL;DR: Euglossine bees may return to a nest from as far away as 23 kilometers in a tropical rain forest and may permit the existence of plant species whose densities have been forced very low by such things as competition and predators on seeds and seedlings.
Abstract: Euglossine bees may return to a nest from as far away as 23 kilometers in a tropical rain forest. These bees apparently forage long distances and visit the same plants repeatedly along a feeding route. They probably promote outcrossing among tropical plants with low population density; therefore, they may permit the existence of plant species whose densities have been forced very low by such things as competition and predators on seeds and seedlings.
TL;DR: In the rat, the injection of insulin or the consumption of carbohydrate causes sequential increases in the concentrations of tryptophan in the plasma and the brain and of serotonin in the brain, and serotonin-containing neurons may participate in systems whereby the rat brain integrates information about the metabolic state in its relation to control of homeostatis and behavior.
Abstract: In the rat, the injection of insulin or the consumption of carbohydrate causes sequential increases in the concentrations of tryptophan in the plasma and the brain and of serotonin in the brain. Serotonin-containing neurons may thus participate in systems whereby the rat brain integrates information about the metabolic state in its relation to control of homeostatis and behavior.
TL;DR: Humpback whales produce a series of beautiful and varied sounds for a period of 7 to 30 minutes and then repeat the same series with considerable precision, and each repeated series of sounds is called a "song."
Abstract: 1) Humpback whales (Megaptera novaeangliae) produce a series of beautiful and varied sounds for a period of 7 to 30 minutes and then repeat the same series with considerable precision. We call such a performance "singing" and each repeated series of sounds a "song." 2) All prolonged sound patterns (recorded so far) of this species are in song form, and each individual adheres to its own song type. 3) There seem to be several song types around which whales construct their songs, but individual variations are pronounced (there is only a very rough species-specific song pattern). 4) Songs are repeated without any obvious pause between them; thus song sessions may continue for several hours. 5) The sequence of themes in successive songs by the same individual is the same. Although the number of phrases per theme varies, no theme is ever completely omitted in our sample. 6) Loud sounds in the ocean, for example dynamite blasts, do not seem to affect the whale9s songs. 7) The sex of the performer of any of the songs we have studied is unknown. 8) The function of the songs is unknown.
TL;DR: It appears that this peptide represents the hypothalamic hormone regulating the secretion of both luteinizing hormone and follicle-stimulating hormone from the pituitaries of several species.
Abstract: A polypeptide isolated from porcine hypothalami stimulates the release of both luteinizing hormone and follicle-stimulating hormone from the pituitaries of several species. This polypeptide has been structurally identified as (pyro)Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH(2) and synthesized. The natural and synthetic materials share biological properties. It appears that this peptide represents the hypothalamic hormone regulating the secretion of both luteinizing hormone and follicle-stimulating hormone.
TL;DR: Subjects learned and recognized patterns which were marginally visible, requiring them to fixate directly each feature to which they wished to attend, and fixed "scanpaths," specific to subject and pattern appeared in their saccadic eye movements.
Abstract: Subjects learned and recognized patterns which were marginally visible, requiring them to fixate directly each feature to which they wished to attend Fixed "scanpaths," specific to subject and pattern, appeared in their saccadic eye movements, both intermittently during learning and in initial eye movements during recognition A proposed theory of pattern perception explains these results
TL;DR: The theory that agriculture originated independently in three different areas and that, in each case, there was a system composed of a center of origin and a noncenter, in which activities of domestication were dispersed over a span of 5,000 to 10,000 kilometers is proposed.
Abstract: I propose the theory that agriculture originated independently in three different areas and that, in each case, there was a system composed of a center of origin and a noncenter, in which activities of domestication were dispersed over a span of 5,000 to 10,000 kilometers. One system includes a definable Near East center and a noncenter in Africa; another system includes a North Chinese center and a noncenter in Southeast Asia and the South Pacific; the third system includes a Mesoamerican center and a South American noncenter. There are suggestions that, in each case, the center and noncenter interact with each other. Crops did not necessarily originate in centers (in any conventional concept of the term), nor did agriculture necessarily develop in a geographical "center."
TL;DR: Herpes simplex virus establishes a persistent, latent infection in spinal ganglia after mice have recovered from posterior paralysis and is replicated when these ganglia are explanted and maintained as organ cultures in vitro.
Abstract: Herpes simplex virus establishes a persistent, latent infection in spinal ganglia after mice have recovered from posterior paralysis. Infectious virus is replicated when these ganglia are explanted and maintained as organ cultures in vitro.
TL;DR: It is indicated that the full genome of murine leukemia virus is present in an unexpressed form in all AKR cells and provide a potentially powerful technique for activating leukemia virus genomes in other cell systems.
Abstract: Cells of embryos of the high leukemic mouse strain AKR can be grown in culture as virus-negative cell lines However, these lines and clonal sublines uniformly have the capacity to initiate synthesis of murine leukemia virus Exposure of the cells to 5-iododeoxyuridine or 5-bromodeoxyuridine induced synthesis of virus in as high as 01 to 05 percent of the cells; many of the cells were producing virus as soon as 3 days after initiation of treatment Induction of virus by these drugs is several orders of magnitude greater than that obtained with any other treatment tested These studies indicate that the full genome of murine leukemia virus is present in an unexpressed form in all AKR cells and provide a potentially powerful technique for activating leukemia virus genomes in other cell systems
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TL;DR: In this article, the authors gave a value of 188,000 for the molecular weight of a stable, catalytically inactive complex of 1 mole hydroxocobalamin and 1 mole of the apoenzyme complex of glycerol dehydrase.
Abstract: In spite of the considerable progress made in recent years toward the understanding of the chemistry and biological function of the cobalt-containing B(12) group of compounds, much of the information still is more descriptive than definitive in nature. In general terms, it is known that the free vitamin forms can function as methyl group carriers and that the 5'-deoxyadenosyl or coenzyme forms serve as hydrogen carriers; but the mechanism of these processes is not understood in detail. More systematic studies of the pure chemistry of these complex molecules containing a carbon-cobalt covalent bond are needed before the biochemist can interpret many of his observations on the enzyme-catalyzed reactions. Even in relatively simple solutions it is difficult to ascertain the state of oxidation of several of the vitamin forms, and these problems are compounded when the reactive thiol compounds and complex proteins of the biological systems also are present. For example, both vitamin B(12r) (the Co(2+) form) and corresponding analogs are known to disproportionate in solution to B(12s) (Co(1+)) and B(12a) (Co(3+)) under a variety of mild conditions (12, 57). This means that in the biological systems it is exceedingly difficult to ascertain the chemical nature of many B(12) intermediates and reaction products. The role of the protein moiety of the various B(12)-linked enzymes in the catalytic processes is little known as is, also, the mode of binding of the B(12) derivative to the protein. These types of questions perhaps can be answered eventually by the crystallographers, whose art is becoming increasingly sophisticated. Note added after preparation of manuscript. In contrast to the values given in Table 4 for the molecular weights of the two dissimilar protein moieties of glycerol dehydrase, a recent report (57a), gives a value of 188,000 for the molecular weight of a stable, catalytically inactive complex of 1 mole of hydroxocobalamin and 1 mole of the apoenzyme complex of glycerol dehydrase. The latter is presumed to contain one equivalent of each of the two dissimilar protein subunits. The original estimate of 240,000 as the molecular weight of the unstable sulfhydryl protein moiety (39) was undoubtedly made on partially aggregated material.
TL;DR: These findings indicate that fibroblasts are able to modulate toward a cell type that is morphologically and functionally close to smooth muscle.
Abstract: Strips of granulation tissue from three different experimental models contract in vitro when treated with substances that induce contraction of smooth muscle. Because the fibroblasts in such tissues have some ultrastructural features typical of smooth muscle, our findings indicate that fibroblasts are able to modulate toward a cell type that is morphologically and functionally close to smooth muscle.
TL;DR: The blood serums of Antarctic fishes freeze at -2�C, which is approximately 1�C below the melting points of their serums, which suggest that this thermal hysteresis results from the adsorption of the glycoprotein molecule onto the surface of ice crystals.
Abstract: The blood serums of Antarctic fishes freeze at -2 degrees C, which is approximately 1 degrees C below the melting points of their serums. This thermal hysteresis is due to the influence of serum glycoproteins. The temperatures of freezing and melting of aqueous solutions of the purified glycoproteins suggest that this thermal hysteresis results from the adsorption of the glycoprotein molecule onto the surface of ice crystals.