Showing papers in "Proceedings of the National Academy of Sciences of the United States of America in 1952"

On the Theory of Dynamic Programming

Abstract: Abstract : The paper is the text of an invited address before the annual summer meeting of the American Mathematical Society at Laramie, Wyoming, September 2, 1954. The contents are chiefly of an expository nature on the theory of dynamic programming.

A Social Equilibrium Existence Theorem.

Abstract: In a wide class of social systems each agent has a range of actions among which he selects one. His choice is not, however, entirely free and the actions of all the other agents determine the subset to which his selection is restricted. Once the action of every agent is given, the outcome of the social activity is known. The preferences of each agent yield his complete ordering of the outcomes and each one of them tries by choosing his action in his restricting subset to bring about the best outcome according to his own preferences. The existence theorem presented here gives general conditions under which there is for such a social system an equilibrium, i.e., a situation where the action of every agent belongs to his restricting subset and no agent has incentive to choose another action.

Transplantation of Living Nuclei From Blastula Cells into Enucleated Frogs' Eggs

Abstract: The role of the nucleus in embryonic differentiation has been the subject of investigations dating back to the beginnings of experimental embryology. At first it was supposed by Roux, Weismann and others that differentiation is the result of qualitative nuclear divisions, different blastomeres thereby receiving the different kinds of nuclei which determine their subsequent differentiation. Later on this theory was disproved by numerous experiments showing that, during early cleavage at least, the distribution of the nuclei can be changed at will without altering the pattern of development. The cleavage nuclei have, therefore, been regarded as identical, and differentiation has been ascribed primarily to the well-known localizations in the egg cytoplasm. This evidence, it should be emphasized, relates only to the early phases of development. During this time it is definitely true that the nuclei in the various blastomeres are equivalent. However, whether they remain equivalent or become differentiated as the various parts of the embryo differentiate has never been tested. The possibility that nuclei might differentiate in response to regional differences in the cytoplasm, and that such nuclear changes might have reciprocal effects on the cytoplasm during cell differentiation, was suggested by Morgan.1 More recently Schultz2– 4 has discussed the problem more fully, indicating the known cytogenetical mechanisms that could account for nuclear differentiation, and Weisz5 has reviewed it in relation to ciliate morphogenesis. Obviously this problem can be solved only by the development of a method for testing directly whether nuclei of differentiating embryonic cells are or are not themselves differentiated. This sort of test could be obtained, as suggested to us several years ago by Schultz, if it were possible to transplant nuclei. Ideally, this type of experiment should be carried out by transplanting the nucleus …

Absolute Rate Theory for Isolated Systems and the Mass Spectra of Polyatomic Molecules.

Abstract: been of fundamental importance in the development of present-day physical theories. As has been stated so many times, the general problem is now solved "in principle" by the quantum mechanics, but the application of the theory to only the simplest systems has been practicable.l, 2 In recent years a very large amount of data has been accumulated on the "mass spectra" resulting from the bombardment of molecules by electrons of energy 50 and 70 volts.3 There is also a significant amount of data on special aspects of the mass spectra of a few polyatomic molecules. A reasonably exact analysis of a mass spectrum would require detailed knowledge of all the electronic states both of the molecule and of all the ions formed from it by removal of electrons and by removal and rearrangement of nuclei. In this paper we present a statistical approach to the problem. Necessarily, assumptions and approximations are required. 'While this theory is in no way complete, we believe it permits the discussion and coordination of a large amount of the available data in terms of the structure of molecules and ions. Knowledge of the effect of low-voltage electron bombardment on molecules, besides being of interest in its own right, has varied applications. It has bearing on the relation of molecular structure to chemical reactivity. It is well known that the major fraction of the effect of high energy radiation on matter, including living systems, is due to the low energy secondary electrons.4 The rate theory presented here should also be applicable to other problems involving isolated systems having a large but finite number of degrees of freedom. The ionization and dissociation of diatomic molecules by electron impact has by now become quite well understood. Hagstrum5 has recently discussed in great detail the mass spectra of a number of diatomic molecules, explaining the formation of the several ions and their kinetic energies in terms of Franck-Condon transitions to the various electronic states of the diatomic ions. Another discussion is that of Stevenson6 who calculated the relative abundance ratios H+/H2+ and D+/D2+ in the mass spectra of hydrogen and deuterium, again using the picture of Franck-Condon transitions to known electronic states. While any discussion of large polyatomic molecules mass spectra must be in accord with these discussions, the direct application of the same methods is impossible.

A Reversible Photoreaction Controlling Seed Germination.

Abstract: * Part of this work was done as a National Research Council Fellow at the University of California, Berkeley. 1 Bonner, J. T., Am. J. Bot., 31, 175 (1944). 2 Skupienski, F. X., Recherches Sur Le Cycle Evolutif Des Certains Myxomycetes, Paris, 1920. 3 Kniep, H., Die Sexualitdt der niederen Pflanzen, Gustav Fischer, Jena, 1928. 4 Raper, K. B., The Quarterly Revie-w of Biology, 26, 169 (1951). 6 Emerson, R., Lloydia, 4, 77 (1941). 6 Raper, K. B., J. Agr. Res., 50, 135(1935). Raper, K. B., Am. J. Bot., 27, 436 (1940). 8Raper, K. B., Growth, The Third Growth Symposium, 5, 41 (1941). 9 Bonner, J. T., and Eldredge, D., Growth, 9, 287 (1945). 10 Bonner, J. T., and Slifkin, M. K., Am. J. Bot., 36, 727 (1949). Olive, E. W., Boston Soc. Nat. Hist. Proc., 30, 451 (1902).

Production of Plaques in Monolayer Tissue Cultures by Single Particles of an Animal Virus

Abstract: Research on the growth characteristics and genetic properties of animal viruses has stood greatly in need of improved quantitative techniques, such as those used in the related field of bacteriophage studies.

On the Early Chemical History of the Earth and the Origin of Life.

Abstract: * This work was done under contract N7-onr 434 Task Order III, Naval Department, Office of Naval Research. 1 Cartan, H., \"Algebraic Topology,\" Harvard Univ., 1949; Wallace, A. D. \"Outline for Algebraic Topology I,\" Tulane Univ., 1949-1950; and Wallace A. D., \"Map Excision Theorem,\" Duke Math. J., 19 (1952). 2 Cf. Tukey, J. W., \"Convergence and Uniformity in General Topology,\" Ann. Math. Studies, Princeton, 1940, p. 53. 3 Cf. Tukey, J. W., loc. cit. 4 See Stone, A. H., \"Paracompactness and Product Spaces,\" Bull. Am. Math. Soc., 54, 977-982 (1948). 6 Cf. Spanier, E. H., \"Cohomology Theory for General Spaces,\" Ann. Math. (2), 49, 407-427 (1948). 6 Cf. Wallace, A. D., loc. cit. 7 See Dowker, C. H., \"t2ech Cohomology Theory and the Axioms,\" Ibid. (2) 51, 278-292 (1950). 8 Cf. Spanier, E. H., loc. cit. ' Cf. Wallace, A. D., loc. cit. 10 Spanier, E. H., loc. cit. and Dowker, C. H., loc. cit. (2) 51, 418. 11 Cf. Eilenberg, S., \"Singular Homology Theory,\" Ibid., (1944), Cor. 9.3. 12P2 A A = fUn Al UE P21. 13 Make use of a homotopy lemma similar to Spanier, loc. cit., Lemma 9.1.

The Structure of Chlorine Hydrate

Abstract: In 1811 Humphry Davy [1] showed that water is a component of the phase that had earlier been thought to be solidified chlorine, and twelve years later Michael Faraday [2] reported an analysis that corresponds to the formula Cl2•10H2O. He surmised that his determination of the chlorine content was low, and later studies have indicated the composition to be close to Cl2•8H2O. Since Faraday's time similar crystalline hydrates of many gases with small molecular volume, including the noble gases and simple hydrocarbons, have been reported. The determination of the structure of ice and the development of an understanding of the nature of the hydrogen bond have strongly suggested that these substances are clathrate compounds, with a tetrahedral hydrogen-bonded framework of water molecules (with O-H•••O = 2.76 A, as in ice) defining cavities large enough to contain the other molecules.

The Isolation and Biochemical Characterization of the Mitotic Apparatus of Dividing Cells.

Abstract: In this communication, the term \"mitotic apparatus\" (abbreviated MA) will refer to the ensemble of structures constituting the \"chromatic\" and \"achromatic\" figures in the classical descriptions of mitosis (e.g., Flemming,I Wilson2). It includes spindles, asters, centrioles, nuclei (before breakdown) and chromosomal structures (after breakdown of the nuclear membrane). The classical pattern of mitosis describes the coordinated behavior of these elements without implying that they are integrated into a physical entity to which such a term as \"mitotic apparatus\" could be applied. Our observations, as will be seen, do indicate the existence of just such a physical association of the various elements, per.mitting their isolation as a single body, and thus the use of the term seems to be justifiable. Heretofore, the physical and chemical study of the MA has been rendered difficult by the necessity of studying it in situ. Most of the earlier information has been adequately summarized by Hughes.3 The most informative avenues of information have been: (a) Staining (e.g., Tahmisian and Brues,4 Mazia, Brewer and Alfert6), (b) polarized light studies (e.g., Inoue and Dan,6 Swann'9), (c) electron microscopy (e.g., Rozsa and Wykcoff7), (d) hydrostatic pressure studies (e.g., Pease8), (e) measurements of anaphase movement of chromosomes (Hughes and Swann9), (f) correlation of dimensional changes of MA with the progress of cytoplasmic division (Dan'0). An enormous literature on the destruction of the MA by antimitotic agents has yielded little insight into its nature. It is evident that the avenues of information have been entirely visual, and that the MA presents exceptional difficulties because it is a structure without a boundary, whose parts are mingled with other cytoplasmic constituents. In the following we describe methods for isolation of the MA in quantity from populations of dividing sea urchin eggs. The somewhat unorthodox methods described were developed after numerous failures with procedures involving disruption of living eggs. Such procedures sometimes yield the MA from a few individuals. Daniellill reports briefly on experiences in liberating the MA from eggs by osmotic rupture.

The Reaction Controlling Floral Initiation

Abstract: Reproduction in many plants and animals is controlled by the length of the night and the cycle of day and night. A dark reaction affords the measure of time and this reaction can be quickly stopped or reversed by light such as that from the rising sun. The reaction is possibly universal in living forms but its more extreme and evident manifestation is recognized to a rather limited extent. Thus flowering of cosmos is determined by long nights while, to casual examination, growth of petunia and tomato is independent of night length. Similarly, reproduction in some species such as goats., turkeys and snails depends on the length of night while the cow and man seem unresponsive. Control of morphogenesis serves better as evidence for the photoreactions in plants. Equivalence of the morphogenic and reproductive controls can be tested by the details of the action spectra for the photoreaction. Thus is established the equivalence of the control for the size of a pea leaf, after it has developed somewhat in darkness and then is exposed briefly to light, with the control of floral initiation in soybean and in barley plants.' Control of bulbing in the onion or color of coat in the varying hare could be followed in a similar way. An understanding of the control reaction, in contradistinction to establishing the equivalence of varied phenomena, came from the study of germination response of lettuce seed to red and near infra-red radiation.2 The reversible photoreaction and an accompanying dark reaction demonstrated for lettuce seed and extended in this study to control of floral initiation follow:

A Case of “Maternal” Inheritance in Neurospora Crassa

Abstract: The inheritance of mutant characters of Neurospora has not previously been found to be influenced by the way in which crosses were made. Whether protoperithecia were furnished by one parent or the other, the result, in so far as the types of progeny recovered were concerned, was the same. In the case to be considered here, however, the inheritance of a slow-growth character, which has been designated as poky, appears to be dependent upon its being carried by the protoperithecial parent. If the strain which furnishes the protoperithecia is considered to correspond to the maternal parent on the basis that it also furnishes the greater part of the cytoplasm from which the ascospores are derived, then this case appears analogous to those which have been described in other organisms (reviewed by Sonneborn [1]). In its failure to be transmitted (when it is carried by the fertilizing parent and not by the protoperithecial parent) the poky character resembles in behavior the petite character in yeast, described by Ephrussi [2] and his collaborators. A simple comparison of the two cases probably cannot be made, however, since the yeast ascospores arise from a mixture of the cytoplasms of the two parents, whereas, in obligate heterothallic strains of Neurospora, it appears probable that such mixing does not occur. [3-5]

The Mechanism of Polymerization of Fibrinogen.

Abstract: Introduction.-Fibrinogen, a rod-like protein of length about 600 A and molecular weight about 350,000, polymerizes under the catalytic action of thrombin to form fibrin, a three-dimensional network structure. A network strand, as seen under the electron microscope, often exhibits uniform width and little curvature over lengths many hundred times that of fibrinogen; the strand width may range from double to many times that of fibrinogen (about 30 A), depending on the pH and ionic strength and other conditions. There is good evidence that the fibrinogen units retain their identity within the strands and that their long axes are aligned in the strand direction. Two intermediates in the polymerization process have been recently identified. The first (f) accumulates when thrombin activates fibrinogen at abnormally low pH (about 5),1 or at abnormally high ionic strength; it has the same gross size and shape as fibrinogen itself, though it has probably suffered the loss of one or more small fragments in the course of activation;2 it polymerizes rapidly when returned to the normal pH and ionic strength. A similar molecule is formed by dissolving fibrin in 3.5 M urea3 or 2 M lithium or sodium bromide.4 The second intermediate (fn) accumulates when thrombin activates fibrinogen in the presence of an inhibitor such as 0.5 M hexamethylene glycol,' 0.5 M lithium bromide, or 1 M urea.' It appears to be a partial polymer of f and is so symbolized; f can be converted to f~ and vice versa by changing the solvent composition;6 and f, dissociates to form f simply upon dilution."7 The conversion of fibrinogen (F) to fibrin is thus pictured as follows:

Auxin-Induced Growth Inhibition a Natural Consequence of Two-Point Attachment.

Abstract: It is characteristic of a great number of biologically active substances that the responses which they elicit are twofold, low concentrations of the material promoting a particular activity, and higher concentrations inhibiting it. This is the case with the auxin-induced growth responses of plants. An active auxin such as indole acetic acid (IAA) brings about and is essential to growth in length of stems, hypocotyls and other plant organs including the Avena coleoptile.

The Isolation and Chemical Properties of the Nucleoli of Starfish Oocytes.

Abstract: The function of several of the discrete protoplasmic structures has been more completely understood where the structure itself has been isolated and studied by direct biochemical methods.' Progress toward the understanding of the chemical nature and of the function of the nucleolus has been hindered by the lack of a suitable technique for the isolation of nucleoli in quantities suitable for direct chemical study. During an attempt to analyze the role of the nucleolus in the growth stages of the oocytes of various forms, a technique for the isolation of nucleoli in quantities suitable for biochemical analyses was developed. This technique and a preliminary report of the chemical composition of the starfish nucleolus is given below. The isolation procedure described has been successfully applied to the oocytic nucleoli of two starfishes: A sterias forbesii and A. rubens; the surf clam, Mactra solidissima; and spider crabs of the genus Maja. The observations and analytical data given below apply exclusively to the nucleolus of Asterias rubens.2 Isola4ion Procedure.-1. Preparation and Homogenization of Material: 15-20 cc. of washed ovaries or exuded eggs in the germinal vesicle stage are allowed to stand for 20 minutes in 100 ml. of water. The tissue is then squeezed through 4 layers of cheesecloth to remove connective tissue and other debris. The cheesecloth is then washed with 100 ml. of water. The combined washing and filtrate are homogenized by being forced through a No. 18-gauge hypodermic needle with a large syringe. The 4omogenate is filtered through 8 to 12 layers of cheesecloth, and the cheesecloth washed with 100 ml. of water. During the development of the technique, it was found that the homogenate generally maintained a pH of 6.0 0.15 without the addition of other buffering agents. This was found to be the optimum pH for isolation, as considerable agglutination of the cytoplasm took place at levels not far above or below pH 6, particularly in the presence of salts. For this reason distilled water was found to be the most suitable isolation medium. Pyrex redistilled water was used throughout, and all operations were carried out in the cold room at 2-4o.