L'effet de la basse température sur l'incorporation de précurseurs des acides nucléiques et des protéines dans les cellules du méristème radiculaire deVicia faba

Summary The uptake of labelled RNA and protein precursors inVicia faba root meristems into nuclei at 4°C is less depressed than in the cytoplasm. Reversion of the normal pattern of incorporation would seem to indicate an inhibition of the RNA transfer from nucleus to cytoplasm.     

Recherches sur le mécanisme de la rétraction du caillot et de la métamorphose visqueuse des plaquettes

Summary The concept, that viscous metamorphosis of platelets and clot retraction is initiated by thrombin and a dialyzable factor was confirmed. Under certain circumstances glucose acts as dialyzable factor. Clot retraction seems to depend upon the catabolism of glucose.     

Action de la triéthylènemélamie sur les mitoses de segmentation de l'œuf de Pleurodèle

Summary Triethylenemelamine (1/400 to 1/12000) induces pseudo-chiasmas and chromosome-breakage in the egg-segmentation mitoses ofPleurodeles waltlii Michah. The primitive effect is stickiness, breakages appear subsequently, but without an interval of time between: the primary physiological and the secondary genetical effect cannot be separated. There are points of breakability, which explains the symmetry of certain fragments. The action is inverted in the epidermal cells of the larvae, where spindle alterations are prominent. Cytodieresis is never inhibited.     

Quelques commentaires sur les méthodes de culturein vitro de jeunes blastodermes de poulet

Summary The relationship between yolk entoblast and the nutritional medium in cultures of chicken blastoderm, classical type, was studied. In addition, some refinements to the research ofNew ^5–7, and some modifications permitting operations from the dorsal side, are proposed.

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Travail subventionné par le Fonds national suisse de la Recherche scientifique.     

Recherches sur la fraction Y des protéines de muscles de Lapin

Summary The proteinic material corresponding toDubuisson's electrophoretic gradient has been prepared by a new method. This fraction migrates as a single peak in the U-tube, but is heterogeneous in the ultra-centrifugation.     

Effets de l'actinomycine D sur le développement normal et sur les modifications expérimentales de la morphogénèse de l'oeuf de l'oursinParacentrotus lividus

Summary In the presence of actinomycin D (20–40 µg/ml), the development of the eggs of the sea urchin,Paracentrotus lividus, is slowed from the late morula and stopped at the blastula stage. The development is immediately stopped in the blastula treated with actinomycin D (20–40 µg/ml). The inhibitory effects of actinomycin D are prevented by deoxyribonucleic acid. Actinomycin D does not exert animalizing or vegetalizing effects. However, the enhancing of vegetalizing action of lithium and the weakening of animalizing effects of zinc ions and Evans blue have been observed in the presence of actinomycin D. These observations may reflect some difference in the state of dependence of differentiation of entomesodermic and ectodermic structures towards the nucleus.     

Communications préliminaires sur les chromosomes des Plécoptères

Summary The chromosomal sets of five species ofPerlodidæ (Plecoptera) are given in the present paper. The sexual chromosomes belong to three distinct types:X-O,X ₁-X ₂,X ₁-X ₂-X ₃. The author shows that these three types are likely derived from the most primitive patternX-Y, by translocation and inversion.     

Action répressive de l'oxygène sur la biosynthèse de la fumarique-réductase d'Aerobacter aerogenes

Summary The cells obtained from anaerobic cultures ofA. aerogenes contain both a hydrogenase and a fumaric reductase, but lack one or several electron transporters necessary for the coupling of the two enzymes. It is possible to measure the fumaric reductase activity of the extracts in the presence of hydrogen, hydrogenase and benzyl viologen, using the Warburg manometric technique. In anaerobic cultures the reductase is an inducible enzyme. In aerobic cultures its formation is strongly repressed by atmospheric oxygen.     

L'évolution de la symbiose chez les Isoptères

Summary An attempt is made to retrace the evolution of symbiotic associations in Blattopteroidea, with particular reference to Isoptera. It seems probable that double symbiosis occured in the common ancestor of Blattids and Termites: intracellular microorganisms of bacteriocytes, xylophagous intestinal Flagellates. Where as actual Blattids, exceptingCryptocercus, have only retained the former, the primitive Termites, exceptingMastotermes, have only kept the latter. Evolved Termites (fam. Termitidae) have in turn lost the symbiotic Flagellates, but have acquired a rich and complex bacterial flora. — Some of these microorganisms, mixed with their aliments, certainly aid digestion (breakdown of cellulose), whilst others, localised at a particular level of the alimentary canal and not found in the alimentary mass, presumably play a different rôle. Furthermore, Protozoa are constantly associated with certains Termites (xylophagous Amoebae, humus-feeder Ciliates of the genusTermitophrya) and may play some rôle in the process of digestion. Finally, an association occurs between fundgus-growing Termites (subfam. Macrotermitinae) and mushrooms (Termitomyces).     

L'action du 2,4-dichlorophénoxyacétate de sodium sur les végétaux

Zusammenfassung 0,5prozentige Lösungen von 2,4-dichlorophenoxyessigsaurem Natrium verhindern das Keimen vonAgrostemma Githago, Hordeum vulgare undTriticum vulgare. Das Wachstum junger Pflanzen der drei Arten wird durch Verpflanzen auf mit 0,5prozentigen Lösungen dieses Stoffes getränktem Sand gehemmt. Schwächere Lösungen gestatten das Wachstum, es ist aber verlangsamt und die Pflanzen tragen Mißbildungen verschiedener Art, die an die nach Einwirkung von Colchicin und Heteroauxin beschriebenen erinnern. Stark verdünnte Lösungen (5·10^–6) beschleunigen das Wachstum und regen die Wurzelbildung an; diese Wirkung ist beiHordeum vulgare besonders deutlich.     

Effets comparés de laβ-propiolactone et du formol sur les propriétés inductrices de l'organisateur chez les amphibiens

Summary -propiolactone-treated dorsal lips ofAmbystoma mexicanum are grafted in the blastocele of young gastrulas. The inducing ability of dorsal lips is not altered. These results are compared with the effects of formaldehyde which suppress the inducing ability. An interpretation of these facts is proposed. The cross-linking reactions which occur between formaldehyde and proteins may be important for the suppressing of the inductive ability by this agent.     

Action de la ribonucléase sur les cellules du carcinome d'Ehrlich

Summary The reduced form of ribonuclease acts on the cells ofEhrlich's carcinoma by producing important changes in the RNA content of cells:(1) First, there is an important synthesis of intracellular RNA and an accumulation of free nucleotides (from the external medium). This phenomenon accompanies the necrosis of the cells.(2) After this first stage begins a rapid degradation of intracellular RNA.Simultaneously, the respiration of cells decreases whilst protein content remains unchanged.The oxidized form of ribonuclease has no action on the cells.

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Aspirant du Fonds national belge de la Recherche scientifique.     

Etude histochimique de l'action des rayons X sur les cholinestérases

Summary Using a histochemical method, we have observed the cholinesterase activity in mice after X irradiation. Both types of cholinesterases were examined: AChE (specific ChE) of megacaryocytes of spleen and bone marrow, and AChE of motor endplates; and non-specific ChE of liver, pancreas and prostate. There is no inactivation of AChE even after 5000 r. ChE is also very resistant: activity is slowed down only 12 h or even a few days following irradiation and the inactivation remains slight. We suppose that the great alterations in cellular permeability caused by irradiation are not correlated with these enzymes.     

Séparation chromatographique de sucres méthylés isomères

Summary The qualitative and quantitative analysis of synthetic mixtures of non-isomeric and isomeric methylated glucoses, as present in the hydrolysate of methylated glucopolysaccharides, has been achieved by hydrogenation of the methylated sugars to the corresponding methylated hexitols, esterification withp-azobenzoylchlorid, and chromatographic analysis on activated alumina.     

Action des enzymes sur la gonadotropine urinaire de ménopause

Summary The action of various proteolytic and glucidolytic enzymes on the biological potency of Human Menopausal Gonadotropin was studied. Trypsin, chymotrypsin, papaïn and glucosidase attack the gonadotropin only after 6 h of digestion. Carboxypeptidase and RDE produce a rapid inactivation.     

La détermination expérimentale de la masse des mésotons par les méthodes d'ionisation

Sans résumé     

Sur l'action de l'acide 2,4-dichlorophénoxyacétique sur la croissance des racines deZea mays et dePisum cultivéesin vitro

Summary (1) A response ofZea mays andPisum roots cultured aseptically to 2,4-dichlorophenoxyacetic acid has been observed.Depending on the concentrationZea mays shows an increase of the growth rate (optimal concentration 10^–11 mol) which turns over to an inhibition (above 10^–7 mol). The curve is similar to that obtained by 3-indoleacetic acid, which proves the phytohormonal character of 2,4-D.(2) ThePisum root is more sensitive than theZea mays root. A concentration of 10^–7 molinhibitsPisum in a high degree, whileZea mays is no more inhibited, thus demonstrating the selective herbicidal action of 2,4-D against isolated roots of Dicotyledons culturedin vitro.