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The changes in volume, weight and specific gravity of tissue samples during fixation in osmium tetroxide or formaldehyde and subsequent infiltration with methacrylate or paraffin were studied in more than 600 tissue specimens. Substantial changes in volume and weight were found, and as a rule the weight changes closely parallelled the volume changes. The influence of the histological procedures on the specific gravity was not so pronounced. During fixation in 1 per cent osmium tetroxide in Tyrode's solution at pH 7.2, a rapid increase of volume took place. Half of the final value was reached after only 15 minutes and the swelling was practically complete after 4 hours. After 24 hours it amounted to 30 per cent. Fixation in formaldehyde likewise caused swelling, which was inversely proportional to the concentration (0.5–16 per cent). With 4 per cent formaldehyde in Krebs-Ringer solution the swelling amounted to 18 per cent after 12 hours, and half of this value was reached in about 30 minutes. Specimens left in the fixation fluids for long periods displayed secondary shrinkage at a rate apparently independent of the concentration of fixative. During dehydration in ethanol, marked shrinkage occurred that averaged 23 per cent for osmium-fixed and 33 per cent for formaldehyde-fixed material. Stepwise dehydration caused less abrupt volume changes, although the end-result differed but little. Among other dehydrating agents, miscible with methacrylate (methanol, acetone, 2-ethoxy-ethanol, dioxane, triethylphosphate), only methanol appeared to give better results than ethanol. Infiltration with methacrylate caused only slight shrinkage, around 7 per cent, regardless of the preceding fixative. During polymerization, however, methacrylate undergoes a 20 per cent reduction of its volume. As far as can be judged from planimetric observations, this shrinkage is to a great extent transferred to the specimens. Paraffin infiltration caused shrinkage of around 30 per cent. With osmium-fixed specimens the fixation temperature influenced the shrinkage during infiltration. Lower fixation temperature gave greater shrinkage. In other stages the temperature had little influence on volume changes. The swelling observed during fixation was found to be due, not to the fixing agents themselves, but to the aqueous media in which they were dissolved. When specimens were placed in saline, Tyrode's, Krebs-Ringer's and sucrose solutions, swelling took place in all of them, including the strongly hypertonic ones. The swelling was inversely proportional to the concentration and was less pronounced in sucrose than in the other medias. Addition of the fixatives, osmium tetroxide or formaldehyde, reduced the swelling to an extent that cannot be explained merely by osmotic action. The addition of macromolecules such as gelatin or dextran was found to reduce the swelling during fixation. The swelling phenomenon could be completely abolished if dextran and sucrose were added in suitable amounts to the osmium tetroxide solution. From the results obtained the following conclusions can be drawn. During conventional preparation procedures for histological specimens, major changes in volume, weight and specific gravity occur. Doubtless, these changes considerably affect the original geometry of the tissues constituents. It is possible, however, to reduce the volume alterations e.g. by addition of colloid-osmotically active substances. 相似文献
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IAN BOOMER ROBIN WHATLEY NIKOLAI V. ALADIN 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1996,29(1):77-85
Fluctuations in the level and chemistry during its history have played a major part in shaping the floral and faunal communities of the Aral Sea. Of the eleven species of Ostracoda (Crustacea) known to have been living in the Aral Sea in 1960, only one survives today due to the anthropogenically induced salinity increase of the past three decades. The origins of a mixed fresh- and brackish-water ostracod fauna are discussed, and it is concluded that some of the major faunal elements must have reached the Aral Sea Basin during a past high water level phase when connection existed with the Caspian Sea. The taxonomic position of key taxa is clarified, and the major elements of the pre-1960 Aral Sea ostracod fauna are illustrated from Holocene sequences. Aral Sea, Ostracoda, Holocene, palaeolimnology. 相似文献
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GUY WOODWARD JOHN B. DYBKJÆR JÓN S. ÓLAFSSON GÍSLI M. GÍSLASON ELÍSABET R. HANNESDÓTTIR NIKOLAI FRIBERG 《Global Change Biology》2010,16(7):1979-1991
The Earth is experiencing historically unprecedented rates of warming, with surface temperatures projected to increase by 3–5 °C globally, and up to 7.5 °C in high latitudes, within the next century. Knowledge of how this will affect biological systems is still largely restricted to the lower levels of organization (e.g. species range shifts), rather than at the community, food web or ecosystem level, where responses cannot be predicted from studying single species in isolation. Further, many correlational studies are confounded with time and/or space, whereas experiments have been mostly confined to laboratory microcosms that cannot capture the true complexity of natural ecosystems. We used a ‘natural experiment’ in an attempt to circumvent these shortcomings, by characterizing community structure and trophic interactions in 15 geothermal Icelandic streams ranging in temperature from 5 °C to 45 °C. Even modest temperature increases had dramatic effects across multiple levels of organization, from changes in the mean body size of the top predators, to unimodal responses of species populations, turnover in community composition, and lengthening of food chains. Our results reveal that the rates of warming predicted for the next century have serious implications for the structure and functioning of these fragile ‘sentinel’ ecosystems across multiple levels of organization. 相似文献
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CHRISTER WIKLUND MAGNE FRIBERG 《Biological journal of the Linnean Society. Linnean Society of London》2011,102(3):635-649
Insects typically spend the winter in a species‐specific diapause stage. The speckled wood butterfly, Pararge aegeria, is unique in having two alternative diapause stages, hibernating as larvae or pupae. In southern Sweden this creates a seasonal flight pattern with four annual adult flight periods: the first in May (pupal diapause), the second in June (larval diapause), and the third and fourth directly developing offspring generations in July and August, respectively. We address the raison d'être of the two diapause pathways by (1) outdoor rearing of cohorts, and (2) performing transect censuses throughout the season for 20 years. We contend that an early start of next season provides a benefit accruing to pupal diapause; conversely, a large proportion of the offspring from adults of the fourth flight peak are unable to reach the pupal stage before winter, providing a benefit accruing to larval winter diapause. The results obtained show that the two hibernation pathways are unlikely to be genetically distinct because of a strong overlap between the two offspring generations, and because sibling offspring from the third and fourth flight periods are likely to choose either of the two hibernation pathways, thereby resulting in a genetic mixing of the pathways. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 635–649. 相似文献
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GÖRAN NILSON MATS HÖGGREN BORIS S. TUNIYEV NIKOLAI L. ORLOV CLAES ANDREN 《Zoologica scripta》1994,23(4):353-360
Phylogenetic relationships for five taxa of Palearctic vipers (genus Vipera ) from the Caucasian region were revealed by cladistic analyses of separate and combined morphological and biochemical characters. The different data sets yielded largely congruent cladograms. Vipera berus from Sweden was included as an ingroup and V. aspis was used for outgroup comparison. For V. kaznakovi and V. dinniki , three and four different sub-populations, respectively, were treated as independent terminal taxa in the analyses. The most parsimonious cladograms confirmed the systematic positions of these populations, discussed in a recent study, and support the hypothesis that the montane populations of the western main Caucasus comprise one polymorphie species: V. dinniki.
Analyses of combined biochemical and morphological data generated two equally parsimonious cladograms (for all ingroups compared), but yielded only one fully resolved topology when ingroups were condensed to the species level: ( berus ((renardi ('ursinii'-eriwanensis )))( dinnikikaznakovi )). 相似文献
Analyses of combined biochemical and morphological data generated two equally parsimonious cladograms (for all ingroups compared), but yielded only one fully resolved topology when ingroups were condensed to the species level: ( berus ((renardi ('ursinii'-eriwanensis )))( dinnikikaznakovi )). 相似文献
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