Pure Stocks Research Articles

Laboratory evalution of a translocation double heterozygote for genetic control of Aedes aegypti

Two pure translocation homozygote stocks, T1/T1 and T3/T3, were used to produce a double translocation heterozygote system designated T1/T3, employing T1/T1 as the male and T3/T3 as the female parent. The double heterozygote showed 73 % sterility when mated to wild females. Tests on mating competitiveness, recombination frequency in the differential segment, insemination rate and inheritance of sterility after release, for four generations in laboratory cages, have been carried out to evaluate the efficiency of this strain as an agent for a population control programme.

Stability of mutations conferring temperature sensitivity on tobacco mosaic virus.

Among several temperature-sensitive mutants of tobacco mosaic virus, reversion to wild-type phenotype is an event sufficiently rare that essentially pure stocks of mutant virus can easily be maintained. The temperature-sensitive phenotype of many of these mutants is stringently expressed. Our data show that most of our mutants are suitable for use in biochemical experiments.

The production of pure stocks of self‐pollinating cereal varieties

SUMMARYThe method of cereal pure stock production used at the Plant Breeding Institute is described. Multiplication from fifty plants to commercial seed stocks takes 5 years; individual ears are inspected each year and an ear‐row/ear‐row progeny system is used. An accelerated system reducing the period of multiplication to 4 years is also described. The advantages and disadvantages of other multiplication methods are discussed.

Genetic heterogeneity of cloned animal virus preparations.

THE procedure used to purify genetically a virus preparation does not guarantee the homogeneity of the derived population1. Genetic purity can be defined by markers characteristic of a given virus. During studies of the selective effects of cloned and uncloned lines of human epithelial cells on a relatively non-cytopathic strain of type 2 poliovirus, MEF12,3, efforts to obtain genetically pure virus stocks failed. We describe here a study undertaken to explain this failure.

Título en español.

Se hizo un estudio para determinar el porciento de cruzamiento natural en el gandur. Se sembraron hileras adyacentes de dos variedades y se encontró que el porciento de cruzamiento fluctuó entre 5.47 y 6.33, con un promedio de 5.80, en una población de 5,328 plantas. En los descendientes de las plantas autofecundadas artificialmente cubriendo las flores con bolsas de nilón, no se encontró evidencia de cruzamiento natural. Los resultados obtenidos en este estudio indican que para mantener la pureza de las variedades y para la producción de semilla de nuevas variedades, es necesario sembrar predios aislados o proteger las flores cubriéndolas con bolsas de nilón para evitar la contaminación de las mismas.

Feather Phaeomelanin Intensity in Buff Orpington, New Hampshire and Rhode Island Red Breeds of Fowl: 3. Relative Quantities of Fractionated Phaeomelanin Pigments ,

IN THE first two reports of this series, studies were conducted to determine the effects of such factors as age, sex and feather growth rate on feather phaeomelanin density (Somes and Smyth, 1965a) and the inheritance of quantitative differences in phaeomelanin pigment from whole feather extracts in three breeds of gold columbian fowl (Somes and Smyth, 1965b). However, studies utilizing whole feather extracts represent a mixture of different phaeomelanin fractions (Nickerson, 1946; Smyth et al., 1951) and provide no information on the relative contributions of each in either pure stocks or cross progeny. Smyth et al. (1951) separated whole feather extracts of both red and buff colored feathers into four different fractions. Two of these, brown I and brown II, appear to be typical melanins, while the other two, called dark purple and red purple by Smyth et al. (1951), are similar to each other and have chemical properties which…

Evidence of prenatal heterosis relating to x-ray induced congential anomalies.

Embryonic mice at 8.5 days gestation from pure C57 and CFl strains and their hybrids were x irradiated to 200 r to determine whether or not prenatal heterosis was manifest. Critenia were the number of normal, resorbed, dead, or anomalous mice seen at 18.5 days in the hybrids as compared with the pure lines. The hybrids at 8.5 days exhibited some degree of heterosis based upon the higher percentage of normal fetuses and the lower percentage of resorptions when comparisons were made with the pure strain parental stocks. For heterosis to be manifest, the hybrids had to overcome the severely deleterious effect of the presence of C57 genes as indicated by the 90% resorptions among this parental stork and only 30% in the hybrids, whereas the CFl showed 39%. Thus there is evidence of more than mere dominance of the more resistant strain genes which leads to heterosis at least by the time of organogenesis. The heterosis for the embryo results in better survival and thus better survival also of the x- irradiation-produced congenital anomalies. (auth)

Chemical Reactions of Antioxidants Used in Vulcanized Rubber

Abstract The work of Farmer and other authors has shown that the oxidation of unsaturated polymers proceeds via primary formed hydroperoxides. The addition of antioxidants, including chiefly compounds of the class of the phenols and secondary aromatic amines, makes it possible to delay to a great extent the chemical changes taking place in unsaturated compounds. The mechanism of the action of phenols in the oxidation has been explained by Bolland. It is difficult to separate from the polymer the reaction products which are formed from the antioxidant by the dehydrogenating action of the polymeric hydroperoxide radical. In view of the fact, however, that the kinetics of oxidation in the presence of added peroxide corresponds to the autoxidation of the unsaturated compound, the reaction between phenols or secondary aromatic amines and organic or inorganic oxidation agents has been studied in detail by several workers. Depending on type, position, and number of the substituents, different reaction products are formed from phenols. Diphenylamine reacts with manganese dioxide to form a mixture of N,N′-diphenylbenzidine and the corresponding quinonedianil. N,N,N′-tri-2-naphthyl-1,2-naphthylenediamine is formed from di-2-naphthylamine with potassium permanganate, whereas under similar conditions phenyl-2-naphthylamine forms N,N′-diphenyl-N-2-naphthyl-1,2-naphthylenediamine. Starting from the deduction that the chemical reaction products of the antioxidants accumulate on the surface of the vulcanized rubber due to decreasing solubility, pure gum stocks of cured natural rubber containing diphenylamine, N-phenyl-1- and 2-naphthylamine have been exposed to atmospheric conditions for 8 months. The dark colored reaction products could be removed mechanically from the surface of the cured goods after wetting with methanol. After evaporation, the residue was taken up in ethylidene chloride and the resulting solution evaporated to dryness. Amorphous mixtures of brown colored compounds were isolated from the vulcanizate containing diphenylamine and N-phenyl-2-naphthylamine, the reaction products of the N-phenyl-2-napthylamine being obtained as a dark colored tar. In addition to other compounds, the presence of the N,N′-diphenyl-N-2-naphthyl-1,2-naphthylenediamine was proved by paper partition chromatography of the resulting azodyestuff obtained from the mixture of the reaction products from phenyl-2-naphthylamine by coupling with diazotized 1-aminonaphthalene trisulfonic acid. The presence of this compound had also been shown by the ultraviolet spectra. In the same manner, small quantities of the N,N′-diphenylbenzidine could be recognized from the corresponding azodyestuff formed from the reaction product of diphenylamine. Due to extensive oxidation, the presence of reaction products could not be proved in any appreciable quantity from the reaction mixture of the phenyl-1-naphthylamine.

Clonal growth of mammalian cells in vitro; growth characteristics of colonies from single HeLa cells with and without a feeder layer.

Two methods for simple and rapid plating of single HeLa cells, human, carcinomatous cells, are described. These result in growth and formation of colonies from each single cell. One of these procedures uses irradiated, non-multiplying "feeder" cells to condition the medium. The second requires more gentle handling of the cells, but otherwise is virtually the same as that used in plating bacteria on semisolid, nutrient media. By extension of these methods, it is possible to isolate single mutant colonies and grow pure clonal stocks of animal cells. These genetically uniform strains are much more homogeneous in their behavior than the parental HeLa cell population. Growth curves obtained from developing colonies are highly reproducible. The most active mutant stocks so far isolated display a generation time of 18 to 20 hours. In pooled human serum HeLa cells assume a highly stretched, ameboid form, with marked motility; whereas growth of the same cells in a variety of non-human sera results in tightly packed, columnar, epithelial-like morphology. The two cell types possess volumes, nuclear cross-sections, plating efficiencies, and generation times which are identical within experimental error, but display widely different cross-sectional areas, suggesting that the basic change occurs in the cell surface. It is conceivable that this change may be related to that which enables the cells of a compact tumor to become invasive. Animal cells subjected to the standard trypsinization procedures which involve mechanical trauma and repeated washings in incomplete media leak large amounts of P and suffer impaired ability to reproduce as isolated cells. Application of the methods described in this paper as a tool for quantitative study of normal mammalian cell growth, physiology, genetics, and biochemistry, and the response of cells to drugs, viruses, high energy radiation, and other agents have been indicated.

Heat conduction and molecular structure in rubberlike polymers

AbstractIn this paper experimentally determined values are reported for the thermal diffusivity (k) of various rubberlike polymers. Corresponding values of the thermal conductivity (W) can be computed from the well‐known relationship, W = kpcp, where p and cp denote the density and specific heat at constant pressure of the composition. Measurements were made on (a) pure gum stocks prepared with natural rubber, Butyl (GR‐I), Perbunan 18, Perbunan 26, Perbunan 35, Buna S (GR‐S), polybutadiene, neoprene GN, polyisoprene, Silastic 160, and Silastic 180; (b) pure gum stocks of the first five rubbers listed under (a) containing in addition 20 parts of a hydrocarbon softener (Bardol), based on 100 parts by weight of the polymer; and (c) the Bardol stocks containing in addition 54 parts of carbon black (Kosmobile 66). From measurements of the rate of change of temperature within a rubber sphere suddenly subjected to a change in its surface temperature, it was found possible to determine the dependence of k on temperature. A satisfactory definition of the “mean” temperature of a sphere under these conditions is described. In a discussion of the effect of chemical composition and structure on heat conduction, the bearing of hindered rotation, cross linking and branching and interatomic bond strength on the results is pointed out. Values are derived for certain other properties of some of the polymers, including their characteristic Debye temperatures, specific heats at constant volume, flexibility of the main valence chains, compressibilities, and sound velocities.

Production of Decorative and Ornamental Rubber Products

Abstract It is proposed to deal with the production of rubber goods which can lay claim to being decorative and ornamental, not according to their classification in a sales catalog, but according to the machines which produce them. CALENDERING One of the difficulties in a works handling rubber qualities ranging from pure gum stocks to the more heavily compounded variety, such as flooring, is to obtain sheets of the same thickness across the width. The wider the sheet the more difficult this becomes. With perfectly cylindrical rolls, the pressure of the rubber bank at the nip will cause the roll to bend, so that a sheet of rubber coming from between such rolls will be thicker in the middle. This variation is overcome by making the rolls a little thicker in the middle by only a few thousandths. However, the amount of bending depends on the type of stock being calendered, so that one calender cannot produce sheet of even thickness from all types of mixings. The greater thickness of the rolls in the middle compared with the ends is referred to as the camber. When the machine is under load, the camber corrects the bending so that the effect is equivalent to using perfectly cylindrical rolls that do not bend. Unless a firm has more than one calender for different types of stock, there is always one class of mix which cannot be the correct thickness right across the sheet. For many classes of goods this variation is not important, but for sheets of rubber intended for flooring to be cut to tiles and pure gum sheet to be cut to thread, it is obvious how important the question of uniform thickness becomes. One cannot expect mechanical pressure during vulcanization to correct this fault or, if it does, other effects are spoilt. For example, the marble pattern on flooring may be spoilt by a sideways flow of rubber under a powerful press, especially where considerable variation was present in the thickness of the calendered sheet. A recent method of correcting camber is to swing the top bowl of, say, a three-bowl calender, so that the axis of one bowl is at an angle to the one immediately underneath. The rollers are, of course, perfectly cylindrical, and only have to be swung through a few degrees.

An X-Ray Investigation of Crystallinity in Rubber

X-ray diffraction evidence has shown that a crystalline structure can be produced in rubber by stretching or by freezing. In the former case, a fiber diagram is generally secured, in the latter, Debye-Scherrer rings. When raw rubber was stretched to moderate elongations and frozen an intense fiber diagram was found, showing that the crystallization proceeded from nuclei set up by the stretching. A series of diffraction patterns illustrating the effect are reproduced. The geometrical conditions of stretching under which ``higher orientation'' occurs in stretched rubber were studied by photometric measurements of the relative densities of the first two equatorial spots. Graphs are included demonstrating the effect of variations in gauge, width, length and elongation of the specimens. Higher orientation occurs when the percent contraction in gauge exceeds the percent contraction in width. The different physical structures of vulcanized pure gum stocks became apparent in the ``higher orientation'' characteristics, although the same diffraction pattern was secured. A correlation of the results with current views on the micellar or secondary structure of rubber and the crystallization of supercooled liquids is attempted.

Low Sulfur Compounding

Abstract Since the beginning of the rubber industry, sulfur dosages used for soft rubber have declined from 20 to 2 or 3 per cent customary today. The decline is still under way, and present sulfur ratios are high in comparison with what is actually required to produce satisfactory commercial vulcanization—fractions of 1 per cent. Vulcanization with extremely low sulfur ratios, the use of selenium and tellurium as auxiliary vulcanizing materials, and the proper type of acceleration required to “cure in” all the sulfur and produce satisfactory commercial results, are discussed. Comparative data, covering many physical attributes, are shown for pure gum and gas black stocks compounded with 3 per cent sulfur on the one hand, and 0.3 and 1 per cent (gas black stock) on the other. Advantages of very low sulfur compounds are less tendency to scorch, better physical properties, better aging, higher resilience and lower power losses, less discoloration, greater resistance to hot solvents, greater abrasion resistance, and less flex-cracking on aging; disadvantages are higher set at low temperatures and reduced capacity to adhere to metals. It seems probable that, in the future, compounding will be based largely on the use of very low sulfur ratios.

National Institute of Agricultural Botany

ONE of the ways in which the Government in Great Britain is aiding agriculture is through grants made to the National Institute of Agricultural Botany. This Institute is doing very important work for the farming community by testing seeds and by encouraging the use of better varieties of plants. The thirteenth annual report, which has just been published, states that the record number of 30,689 samples of seeds was tested in the year ended July 31, 1932, at the Official Seed-testing Station. Trials with oats showed that one variety, Golden Rain II, gave the best results, although it is not widely grown; and that in Wales the variety popularly believed to be the best (Record) was significantly inferior to the three other varieties tested. The outstanding problem in the home beet-sugar industry is to improve the yields of beet and of sugar per acre; whereas the average for Europe is about 1½ tons of sugar per acre, in Great Britain it is only slightly more than 1 ton. The Institute has been attacking this important problem and has demonstrated how much these yields depend upon the variety grown. Trials extending over three years have shown differences of nearly 20 per cent between varieties in use by farmers, and Kleinwanzleben E has in general been found to be by far the best; at one centre it gave no less than 3 tons of sugar per acre. As a result of this work, it is now possible to recommend twelve different strains for use in the British Isles. Other activities of the Institute include the provision of pure stocks of cereal seed, the improvement of varieties of potato in respect of yield, and, especially, of immunity from disease, and the prevention of the use of more than one name for the same variety.

Stearic Acid in Litharge-Cured Rubber Compounds

Abstract Although an organic acid is essential to vulcanization with litharge, smoked sheet usually has enough natural acid for full activation. For example, when 5 per cent stearic acid (or similar softeners) was added to a standard smoked sheet in a high zinc oxide stock the properties were lowered. On the other hand, a “low-grade” rubber, Lapori, was greatly improved in a high zinc oxide formula by stearic and by other acids. Acidic softeners in a high zinc oxide stock increased set, even when they promoted vulcanization. In a pure gum litharge formula with smoked sheet, 1 per cent stearic had but little effect, while in a high gas black formula, 4 per cent stearic raised the tensile (probably due to improved dispersion) but had no marked effect on rate of cure. When litharge was used as the activator for mercaptobenzothiazole, stearic acid had but little effect either in pure gum or high gas black stocks. On the contrary, when zinc oxide was used proper curing was highly dependent on stearic, especially with gas black. The litharge-mercaptobenzothiazole compounds with gas black in tread stock proportions, either with or without stearic, yielded a high tensile over a wide range of cures.

The maintenance of pure and vigorous stocks of varieties of the potato (Revised Edition, 1927) (Board of Agriculture for Scotland, Edinburgh) price: one shilling

The maintenance of pure and vigorous stocks of varieties of the potato (Revised Edition, 1927) (Board of Agriculture for Scotland, Edinburgh) price: one shilling