Showing papers by "Dartmouth College published in 1969"

Nitrification: importance to nutrient losses from a cutover forested ecosystem.

Abstract: The nitrate concentration (weighted average) in stream water from an experimentally deforested watershed increased from 0.9 milligram per liter before removal of the vegetation to 53 milligrams per liter 2 years later. This nitrate mobilization, presumably due to increased microbial nitrification, was equivalent to all of the other net cationic increases and anionic decreases observed in tae drainage water.

Gill Dimensions for Three Species of Tunny

Abstract: 1. Estimates have been made of the total area of the secondary lamellae in the gills of skipjack tuna ( Katsuwonus pelamis ), yellowfin tuna ( Thunnus albacares ), and bluefin tuna ( T. thynnus ). A sampling method is described which takes into account the variation in size and spacing of the secondary lamellae in different portions of the sieve. 2. Twenty-six specimens in the weight range 1-40 kg. were examined and analysed by logarithmic plots of different gill dimensions against body weight. A good fit was found to the general equation A = aW b . 3. The slope ( b ) of the regression line for the total area ( A ) against body weight ( W ) was found to be about 0.85 for all three species. This relationship is similar to that (0.81) between oxygen consumption and body weight for a large number of species of teleost fish. 4. The corresponding regression coefficients for the relationships between body size and average area of a secondary lamella, number of secondary lamellae per millimetre and total filament length were +0.53, -0.08 and +0.38 respectively. 5. A comparison is made between the three species of tunny and the limited data available for size ranges of other teleosts. On the basis of values obtained by extra polating the regression lines, it is concluded that the tunny has a larger gill area per unit of body weight than any other fish so far investigated. This is mainly due to the large total length of the gill filaments and the very close spacing (up to 120 per mm. have been measured) of relatively small secondary lamellae. 6. It is concluded that the extensive gill area of the tunny is related to its very active mode of life.

Interrelationships of Selenium, Cadmium, and Arsenic in Mammalian Teratogenesis

Abstract: Cadmium sulfate and sodium arsenate injected into pregnant hamsters are independently teratogenic. Sodium selenite which is not teratogenic under similar conditions does provide significant protection against the malformations induced by cadmium or arsenic when injected simultaneously with either of these teratogens. The effect of a time interval between the injection of cadmium and selenium revealed that the protective effect of selenium was still marked at a 30-minute interval but decreased markedly at two- to four-hour intervals. At the 30-minute interval the protective effect was more marked when the selenium was injected first rather than the reciprocal method.

Isopropyl N-Phenylcarbamate Affects Spindle Microtubule Orientation in Dividing Endosperm Cells of Haemanthus Katherinae Baker

Abstract: The mitotic inhibitor isopropyl N-phenylcarbamate (IPC) effects changes in the ultra-structure of the dividing endosperm cells of Haemanthus katherinae. In cells treated with 10 p.p.m. IPC for 0.5-2 h the microtubules lose their parallel alignment and become oriented in radial arrays. These radial arrays are interpreted as micropoles of the spindle apparatus and are thought to be the focal points for the chromosomes as they aggregate into micronuclei. Thus, IPC has a markedly different effect on the structure of the spindle apparatus than colchicine, which is observed at concentrations of 50 p.p.m. for 1 h to destroy the microtubules in Haemanthus. The structure of the microtubules appears unaffected by IPC since those from control and treated cells are similar in diameter (22 nm), in degree of staining, and in sensitivity to the fixation. In addition, the chromosomes and cytoplasmic components such as mitochondria, plastids, dictyosomes, elements of the endoplasmic reticulum, and ribosomes are not structurally modified by treatment with IPC.

New Product Adoption in Industrial Markets: A Framework for Analysis:

Abstract: For marketing managers in firms whose customers are other firms, and for researchers interested in industrial buying behavior, it would be helpful to understand the process by which firms decide to...

The Dynamics of Aquatic Ecosystems

Abstract: Publisher Summary This chapter aims to identify the problems of studying whole ecosystems. It explores whether the detailed studies of components of the systems have increased the understanding of the working of the whole systems. The development of the understanding of the dynamics of ecosystems largely considers the progressive clarification of the concepts of production and the factors controlling food uptake, assimilation, and metabolism. Over the years, the tropho-dynamic model of Lindeman has served well. Most organisms can be placed in one trophic level or another on the basis of their main feeding habits. It is observed that knowledge of the magnitude of primary production is essential in understanding of any ecosystem. Of all the aquatic animals, emphasis is largely on fish. Techniques are available for determining population density, age structure and growth rates, and considerable progress has been made in understanding the principles governing their feeding and metabolism.

Recent volcanic and fumarolic activity at Santiaguito volcano, Guatemala

Abstract: Santiaguito, an extrusive domal complex in southwestern Guatemala has recently exhibited renewed domal growth, as much as 50 meters vertically in the first twelve months of growth. Synchronous with this activity, near the other end of the complex 1.3 km distant, there are pyroclastic eruptions. Ninety percent of the extensive hot lumarolic emission at Santiaguito is concentrated near the active pyroclastic vent, although numerous other lumaroles are found including a group of particularly hot vents associated with the current dome extrusion. Description and tabulation of chemical and mineralogical characteristics of sublimates and condensed gas from fumaroles at eight localities on the mountain illustrate the essential similarity and also the minor differences. The differences are in many instances related to volume of gas, the amount of rainwater dilution, and amount of oxidation of the gases along their path.

American Rings and English Mules: The Role of Economic Rationality

Abstract: Introduction, 25. — Observed investment behavior, 27. — The relative advantages of rings or mules in the United States and Great Britain, 29. — The role of cotton prices, 34. — Relative factor costs as a function of counts spun, 39. — Costs and benefits, 42.

Kinetics of incorporation of structural proteins into Sindbis virions.

Abstract: The morphogenesis of Sindbis virus was studied by determining the kinetics with which newly synthesized nucleocapsid and envelope proteins appeared in virions released into the extracellular medium. Assembly of the nucleocapsid was more rapid than modification of the cellular membrane by the addition of the viral envelope protein. However, both viral structural proteins were efficiently incorporated into virions; a 0.5-hr pulse-labeling period resulted in the release of maximally labeled virus during the next hour. When protein synthesis was inhibited, release of virus soon declined even though large amounts of both viral structural proteins were present within the cell and ribonucleic acid replication was unaffected.

The synteratogenic effect of lead and cadmium.

Abstract: Bleisalze verursachten fotale Missbildungen der Kaudalregion, wenn sie trachtigen Gold-hamstern am 8. Tage injiziert wurden. Kadmiumsalze hingegen verursachten hauptsachlich Gesichts-, Augen und Gehirndefekte. Die hier beschriebenen Befunde zeigen, dass die Kombination dieser beiden Teratogene zu wesentlich reduzierten Gesichtsmissbildungen, aber erheblich potenzierten Kaudalskelettmissbildungen (Sympus) fuhrt.

The permeability of the hamster placenta to radioactive cadmium

Abstract: Studies on the permeability of the mammalian placenta to teratogenic agents during the early critical stages of embryogenesis have been relatively few. Most of these studies have been done in the pregnant rabbit, in which the unusually large size of the blastocyst makes it possible to obtain samples of blastocyst fluid for analysis. Thus, investigations have been done on the permeability of the rabbit blastocyst wall to trypan blue and other teratogenic azo dyes (Ferm, 1956), changes in blastocyst sugar content following maternal administration of insulin (Curry & Ferm, 1962; Lutwak-Mann, 1962) and the effect of thalidomide and other agents on the implanting rabbit blastocyst (Lutwak-Mann & Hay, 1962; Hay, 1964; Fabro, Smith & Williams, 1965; Keberle et al. 1965; Fabro, Hague & Smith, 1967). However, the much smaller size of the rat, mouse and hamster blastocysts makes comparable studies in these species extremely difficult and most attempts to investigate the placental permeability to teratogens in these animals in the early critical stages of embryogenesis have been directed toward histological, histochemical and radioautographic techniques.

Inhibition of Interjacent Ribonucleic Acid (26S) Synthesis in Cells Infected by Sindbis Virus

Abstract: The interrelationship of viral ribonucleic acid (RNA) and protein synthesis in cells infected by Sindbis virus was investigated. When cultures were treated with puromycin early in the course of infection, the synthesis of interjacent RNA (26S) was preferentially inhibited. A similar result was obtained by shifting cells infected by one temperature-sensitive mutant defective in RNA synthesis from the permissive (29 C) to the nonpermissive (41.5 C) temperature. Under both conditions, the viral RNA produced appeared to be fully active biologically. Once underway, the synthesis of viral RNA in wild-type Sindbis infections did not require concomitant protein synthesis.

The concept of energy efficiency in primary production1

Abstract: The use of efficiency factors in primary productivity studies is discussed. A coefficient kb is defined which measures the contribution of photosynthetic processes to the total optical attenuation coefficient. It is shown that to a first order approximation, kb at any depth is given by the ratio of the primary production to the incident radiation at that depth, when both are expressed in calories. Values of kb are calculated for two stations in St. Margaret’s Bay, Nova Scotia. At any depth, kb depends linearly on the chlorophyll concentration at that depth. Errors involved in measuring kb are discussed and suggestions made for increasing precision. It is suggested that kb could be used as an index to compare the primary productivity of waters and that the regression of kb on the chlorophyll concentration could be used as a predictive tool in primary production research.

Regulation of Mitosis: II. Interaction of Isopropyl N-Phenyl-Carbamate and Melatonin

Abstract: Earlier studies on the effects of the herbicide isopropyl N-phenylcarbamate (IPC) on mitosis revealed blocked metaphases, multinucleate cells, giant nuclei and an increase in number of partly contracted chromosomes. It was assumed that IPC, like colchicine, was causing these effects by disruption of the spindle apparatus by destroying the spindle microtubules. The animal hormone melatonin causes an increase in birefringence of the mitotic spindle in animal cells, presumably by increasing the number of microtubules. We have studied the effects of IPC, melatonin, and combinations of the two on mitosis in dividing endosperm cells of the African blood lily (Haemanthus katherinae Baker) in vivo by phase-contrast and polarization microscopy. Both qualitative and quantitative data are presented. Interpretation of these results has been aided materially by a time-lapse cinemicrographic analysis of dividing cells subjected to 1 and 10 p.p.m. IPC (unpublished) and by an accompanying fine-structural analysis of untreated and IPC-treated cells. Mitosis was disrupted by 0.01-10 p.p.m. IPC, the severity of the effect depending on both concentration and stage of mitosis of the cell at the time of treatment. Concentrations of IPC that caused cessation of chromosome movement also caused loss of birefringence of the mitotic spindle. Melatonin increased birefringence of the mitotic spindle in these plant cells and partly nullified the adverse effects of IPC. The results of this study demonstrate that the herbicide IPC, under our conditions, causes disruption of mitosis and loss of birefringence of the spindle. And it has been established that an animal hormone is capable of increasing the birefringence, and presumably the number of microtubules, of the mitotic spindle in dividing endosperm cells of a higher plant. Although melatonin is capable of partly nullifying the effects of IPC, a competitive antagonism is not postulated.

Traditional safety measures and accidental poisoning in childhood

Abstract: Although few drugs, surgical technique, and public health measures are put into widespread use today without rigorous testing and evaluation, such assessment of efficacy is the exceplion rather than the rule with countermeasures against accidental injury. Many countermeasures now in use have never been evaluated; others continue in use long after they have been proved to be ineffective. Driver education, for example, is being widely adopted in the face of mounting evidence that it does nothing to prevent accidents. Programs of "home safety education" continue to be formulated despite considerable evidence that they do not produce the intended results. This unconcern for--if not downright resistance to--systematic research on effectiveness has several consequences: (1) It permits programs of questionable value to absorb funds and manpower that might better be used in developing effective programs. (2) It precludes the possibility of a cost-effectiveness approach, which promises to be at least as useful in injury control as it has been in other areas of social concern. (3) It develops and strengthens vested interests connected with established programs--and thus it increases the resistance against objective evaluation. (4) It lulls the lay public into a false sense of security, since the public is likely to assume that accident countermeasures have the same degree of validity as other public health measures. The signal contribution of the paper that follows lies in its challenge of a "safety measure" that has long been accepted and disseminated by professionals and laymen alike. Although the population studied is both small and in some respects atypical, the findings are strong enough to warrant further study of larger and different populations. The methodology employed is also worth emulating. Recognizing the bias inherent in medical records and the difficulty of obtaining valid and representative responses to mail questionnaires, the investigator resorted to both interviewing and observation, which, though unquestionably expensive, are probably the most effective methods of data collection available to the research worker studying accidental injury. Language: en

Thyroxine metabolism and thyroid function in the cold-adapted rat.

Abstract: Thyroid function and thyroxine (T4) metabolism were assessed in rats maintained at 4 or 22 C for at least 3 months. In the coldadapted rat, thyroidal uptake of iodine was increased up to 3-fold. Since total glandular iodine was unchanged, thyroid secretion rate was presumed to be similarly increased. The metabolism of T4 was studied in rats (KC104-treated to prevent 131I uptake by the thyroid) iso topically equilibrated with 131I-T4 of known specific activity. Cold-adapted rats excreted less iodide in urine than did controls, when receiving twice the dose of T4, and not significantly more than controls when given 4 times the dose, although the latter dose raised the serum T4 level above normal. The apparent reduction in the rate of deiodination was not due to changes in the intrinsic deiodinating activity of tissues, or to changes in the T4-binding activity of serum. Total and free T4 levels were not altered. The total turnover of T4 was increased due to a marked increase in the clearance from plasma thro...

Transplacental infection of rats and hamsters induced by oral and parenteral inoculations of H‐1 and rat viruses (RV)

Abstract: An aim of the present investigations was to use recently isolated strains of H-1 and RV, which had been subjected to a minimum of laboratory passages, to induce transplacental infection orally in order to replicate natural infections in rats, the natural hosts, as well as in hamsters, which are subject to “spontaneous” infection with these agents. H-1 virus had a remarkable ability to penetrate both the gut wall and placental barrier and infect fetuses within 24 hours of oral inoculation of pregnant hamsters, whereas such infections could be induced in rats only by parenteral inoculation. However, rats were susceptible to fetal infection with RV given orally. The pathogenesis of infection was somewhat different with the two viruses. RV, in contradistinction to H-1, proliferated in maternal organs and possibly in the placenta for several days before invading the fetus. Both H-1 and RV were alike in being transported in the blood in close association with erythrocytes. All fetuses invaded by either agent developed widespread infections prior to death as shown by the presence of intranuclear inclusions and cytolytic effects. Placentas remained intact and viable even after resorption of attached fetuses. The health of all mother animals was unaffected. One special strain — HHP — was the only RV strain to induce transplacental infection orally in hamsters. The various attributes of these parvoviruses that make them particularly favorable agents for the study of transplacental infections are discussed.

Submarine End Moraines and Associated Deposits on the Scotian Shelf

Abstract: A submarine end-moraine complex occurs on the Scotian Shelf south and east of Halifax at 30 to 40 km offshore. It extends as a belt of low ridges which lies parallel to the present coast. Some of the larger individual ridges extend up to 55 km in length, with a slight arcuate pattern, and are an average of 50 m in height above the underlying bedrock. The full extent of the system has not been determined; however, a cursory examination indicates its occurrence along at least 500 km of the coast, in water depths ranging from 70 to 200 m. The moraine pattern is not revealed on the published bathymetric chart, because the ridges are to a large degree sub-bottom features, masked by ponded clay and silt deposits. However, the extreme peaks of some ridges may crop out slightly above the clay and silt of the bottom, so that their pattern must be resolved by detailed geologic mapping. The materials forming the exposed portions of the ridges range from relatively unaltered to completely reworked glacial debris, depending on the depth of water in which they occur. Resolution of the moraine pattern is greatly enhanced when the ridges are mapped as sub-bottom features, using high-frequency echograms obtained at closely spaced intervals. The degree of penetration with such an echo-sounder is limited essentially to the base of the clay, but the full profile of the moraines above the underlying bedrock is revealed by low-frequency, continuous seismic reflection profiles. Sub-bottom records and textural data on bottom samples indicate the occurrence of stratified proglacial deposits associated with the moraines.

Uptake and storage of Thorotrast by the rodent yolk sac placenta: an electron microscopic study.

Abstract: Electron microscopy was used to investigate the uptake and storage of electrondense particulate matter by the rodent yolk sac placenta. Pregnant hamsters were given single intra-uterine injections of Thorotrast on day 13, 14 or 15 of gestation and killed at intervals between 15 minutes and 48 hours thereafter. Electron microscopic examination of yolk sacs removed from the injected animals revealed the rapid and progressive uptake of the tracer particles by the visceral epithelial cells of these fetal membranes. Pinocytic vacuoles (phagosomes) containing Thorotrast were visible in the apical cytoplasm of epithelial cells as early as 15 minutes after injection and became increasingly abundant in these cells at later post-injection intervals up to 18 hours. Epithelial cells which became fully engorged with Thorotrast vacuoles exhibited various pathologic changes, possibly caused by the interference of the metabolically inert metal particles with intracellular digestive mechanisms (the lysosome system). There was no evidence, however, of transport of Thorotrast particles through or between the yolk sac epithelial cells. The connective tissue spaces and blood vessels of the yolk sac, as well as underlying fetal compartments, were free of the tracer particles at all observed intervals after injection.

Cytogenetic and Phylogenetic Studies in Carnivora

Abstract: Let us look at the carnivores from the point of view of their presently accepted taxonomy and phylogeny and see how the study of their chromosome constitution fits with the accepted scheme, or where it may give us something new to consider. The earliest Carnivora were the creodonts which appeared in the Paleocene about 75 million years ago. By the Eocene, 60 million years ago, a branch called the Miacidae was flourishing. The creodonts subsequently became extinct, but toward the end of the Eocene the Miacidae diverged into three major branches of the Carnivora (Fig. 1*): these are first the Feloidea, which include the cats, the hyenas, and the mongooses and civets; the second the Canoidea, which include the raccoons, bears, dogs, wolves and foxes, and the weasels, minks, martens, badgers, skunks and otters; and the third the Pinnipedia or marine carnivores, which include the walruses, seals and sea lions. The Pinnipedia are, today, generally not included with the Carnivora but are placed in a separate Order. They did, however, arise from the Canoidea and still retain close serological (Leone and Wiens, 1956; Pauly and Wolfe, 1957) and chromosomal relationships. The latter can be seen in the figure by comparing the diploid number, fundamental number and marker chromosomes with those of the Canoidea.