Growth of calvarial width. An experimental investigation in rabbits

This investigation was conducted to analyze growth in width of the rabbit calvarium. 15 male New Zealand white rabbits were subjected to regular stereometric examinations from 31 to 141 days of age after implantation of tantalum bone markers. The sagittal suture complex, i.e. the interfrontal and interparietal sutures, and the bilateral temporal sutures demonstrated similar growth rates in magnitude which moderately decelerated throughout the observation period. Transverse growth exhibited local growth fluctuations and short-term negative growth values in a well-balanced manner.     

Cytology of experimental mesotheliomas induced with crocidolite asbestos

The cellular features of 12 pleural and 5 peritoneal effusions, derived from experimental mesotheliomas induced with crocidolite asbestos in white rats, are described. The fluids were obtained 11 to 18 months after the introduction of asbestos into the body cavity. The morphologic characteristics of the cytoplasm, nuclei and nucleoli in the neoplastic mesothelial cells were studied using the Pappenheim, periodic acid-Schiff and Smetana stains. Nearly all effusions examined contained numerous normal and abnormal mitoses. Cell configurations suggestive of amitotic divisions were also observed. The study of the morphologic features of mesothelial cells in effusions in experimental asbestos-induced mesotheliomas may contribute to the understanding of the neoplastic transformation of the mesothelium.     

中国旧石器时代石球的实验研究

石球是一种旧石器时代分布极为广泛的石质工具,有关其形制、制作与使用还存在较大的探索空间。其形制包括一般打制石球与琢制滚圆的石球。中国发现石球按大小可以分为两个类型,较大者多属于旧石器时代早中期,较小者多属于旧石器时代晚期及以后时期,本文讨论侧重前者。实验研究显示,石球生产是一项时间成本高昂的活动,如果加上琢制过程,所需要时间远多于手斧生产。旧石器时代早中期石球的大小与质量存在明显的偏向性,与成年男性手掌大小一致,这支持石球可能是直接握持使用的。投掷使用实验表明,平均质量与大小、形制规整的石球最有利于用手抓握投掷。结合考古材料中石球集中发现的状况与伴生动物化石进一步支持石球很可能是一种狩猎工具。不过采用石球狩猎距离较短,杀伤力有限,且更依赖机会,有较高风险。     

An investigation of non-steady-state algal growth. I. An experimental model ecosystem

In order to test rigorously the transient behaviour of mathematical models of algal growth, detailed laboratory data sets with good temporal resolution are required. A series of algal growth experiments was conducted in transient conditions. Monoculture growth of, and competition for nutrients between, three contrasting species of phytoplankton (the diatom Thalassiosira pseudonana, the harmful flagellate Heterosigma carterae and the toxic dinoflagellate Alexandrium minutum) were investigated in different temperature, light and nutrient regimes. Although growth dynamics were qualitatively similar in batch culture, quantitative differences were evident in the growth response of the different species when grown in single yield-limiting nutrient conditions in identical physical conditions. Quantities such as the carbon:nitrogen (C:N) ratio and C and N per cell varied between species and within species under different growth conditions. Such results have particular significance to the development of mathematical models, which commonly represent algal populations as a single homogeneous group using a single currency such as numbers, C or N. Changes in light and temperature regime influenced algal growth: Alexandrium failed to grow at low temperatures, while specific growth rates of Thalassiosira were more sensitive to changes in temperature than those of Heterosigma. Changes in the dominant organism(s) and/or its size or nutrient status may influence the transfer of nutrients within the food web. Commonly, mathematical models make cell growth a function of a single yield-limiting nutrient. Decreased growth rates and high residual nutrient concentrations in competition experiments indicate that this approach is unlikely to be successful in conditions of limited supply of more than one nutrient, where multiple nutrient stresses will be significant.      

云南居民区鼠类体外寄生蚤物种多样性调查

【目的】了解云南居民区鼠类寄生蚤的群落结构和空间分布特征。【方法】根据云南不同经纬度、 海拔等自然环境条件, 于2007年4月-2012年11月, 选取云南17个县(市) 居民区作为样区, 系统开展鼠类体外寄生蚤的调查, 运用群落结构指标对居民区鼠类寄生蚤的群落特征和沿环境梯度的空间分布进行研究。【结果】结果显示： 在调查的17个县(市)室内共检获鼠类体外寄生蚤521头, 隶属4科7亚科9属12种。居民区寄生蚤的纬度和垂直分布类似, 低纬度和低海拔范围的种类相对较少, 印鼠客蚤和缓慢细蚤是室内寄生蚤的优势种。相对纬度和海拔较高的区域, 居民区寄生蚤种类增多, 但优势种不突出; 在经度水平分布上, 蚤种类于99°~101°E经度带形成一个高峰, 室内寄生的优势种印鼠客蚤和缓慢细蚤几乎在所有经度带都可见到分布, 显示了较宽的生态幅。另外, 居民区寄生蚤物种丰富度和多样性指数水平分布（纬度）和垂直分布呈现为单峰格局, 总体显示随着纬度和海拔的升高, 先升高后降低的分布特征, 而在另一个水平分布（经度）, 则呈现由西向东呈递减的趋势。【结论】研究认为, 云南居民区蚤类的空间分布表现为独特的地理区域特征, 气候环境、 森林植被和人类生活生产方式通过影响蚤类栖息生境来影响蚤类的分布。     

An experimental investigation of interactions in snail-macrophyte-epiphyte systems

Summary An experimental investigation under field conditions of enclosures containing freshwater pulmonate snails, the macrophyteCeratophyllum demersum and epiphytes, produced evidence of beneficial interactions.Ceratophyllum growth, measured in terms of stem length, numbers of leaf-nodes and growing tips and leaf survival was significantly enhanced in the presence of snails. This effect was attributed to the increased availability of plant nutrients of snail origin, such as phosphates and ammonia, as well as to the snails' action as “cleaning symbionts” in reducing the density of bacterial and algal epiphyton potentially deleterious to macrophytes. Principal component analysis revealed both seasonal and treatment effects of snail grazing on algal epiphyton. Small adnate algal species (e.g.Cocconeis placentula) survived grazing and benefited from the removal of larger, competitor, species. Snail densities increased in all treatments, despite high (86%) juvenile mortality. It is concluded that freshwater pulmonate snails are strong interactors in lentic habitats, enhancing the growth ofCeratophyllum and producing characterisic epiphyte communities. This benefits not only the snails, but also the plants and epiphytes that are associated with them. Thus the interactions between these component parts of the community can be considered as mutualistic.     

Transport of bacteria in porous media: I. An experimental investigation

The convective transport of concentrated suspension of bacteria in porous media is of interest for several processes such as microbial enhanced oil recovery and in situ bioremediation. The parameters which affect the transport of the bacterium Bacillus licheniformis JF-2, a candidate microorganism for microbial enhanced oil recovery, were investigated experimentally in sandpacks. Bacteria retention and permeability reduction occurred primarily in the first few centimeters upon entering the porous medium. In downstream sections of the sandpack, the permeability reduction was low, even in cases in which high cell concentrations (10(8) cfu/mL) were detected in the effluent. The effect of (i) addition of a dispersant, (ii) linear velocity of injection, (iii) cell concentration, (iv) salinity (v) temperature, and (vi) the presence of a residual oleic phase were determined experimentally. A lower reduction in permeability and a higher effluent bacterial concentration were obtained in the presence of dispersant, high injection velocities, low salinities, and at a higher temperature. Macroscopic measurements at different linear velocities and in the presence or absence of dispersants suggest that the formation of reversible microaggregates and multiparticle hydrodynamic exclusion may be the primary mechanisms for bacterial retention and permeability reduction. (c) 1994 John Wiley & Sons, Inc.     

Cytotaxonomic study of ferns of Yunnan,southwestern China

A cytotaxonomic study was made of 90 fern species of Yunnan, southwestern China, based on collections from northwestern, central, and southwestern Yunnan and a few Cheng's collections. The results verified most of the formerly reported basic chromosome numbers of Chinese genera, and recorded for the first time the basic numbers ofGymnogrammitis andSorolepidium and Chinese members of several other genera. Cytotaxonomy of some problematical genera was discussed. Biogeographical relationships between Japanese, Chinese, and Himalayan ferns were compared with special reference to local cyto-reproductive variations inConiogramme, Deparia, Onychium, andPteris cretica. The present evidence indicates that most triploid species examined are agamosporous, as general in filicalean ferns, and also suggests the sexual 32-spored sporogenesis inHypodematium crenatum andSorolepidium graciale as in Lindsaeaceae.     

Higher plants as bioindicators of metal contamination from Shangdong abandoned karst bauxite,southwestern China

• Bauxite mining on karst generates numerous ecological and environmental problems, including metal pollution, water and soil erosion and destruction of vegetation. Among these, the most important environmental problem is soil metal pollution. Higher plants have a great ability to adsorb metals and can be used as biological indicators. However, the study of bioindicators for soil contamination in karst bauxite is not clear.
• Plants and their soil were collected from an abandoned karst bauxite area at Shangdong, Guizhou Province, southwestern China. Plants were collected and identified as Pteris vittata, Pinus massoniana, Miscanthus floridulus, Coriaria nepalensis, Artemisia argyi and Senecio scandens.
• The content of metals in plant roots were in the order: P. vittata > M. floridulus > C. nepalensis, other plants roots had no consistent pattern. Concentrations of metal in plants (P. vittata and M. floridulus) and soil were: soil > root > leaf > stem. Levels of metals in soil samples easily exceeded background values, indicating that soil had been contaminated. Al and Fe were highest in soil samples of P. vittata, with a good correlation.
• Results show that the metal content determined in plants is relatively high, particularly in P. vittata. Data also suggest that P. vittata colonies were able to tolerate and accumulate high levels of metal elements, which evidences their suitability for use as bioindicatord of soil metal contamination caused by mining activities.

     

Bacteria and phosphorus regeneration in lakes. An experimental study

The aerobic decomposition of the green alga Chlamydomonas reinhardii by a mixed population of lake bacteria was studied in batch and chemostat cultures. Bacterial chemostats were supplied with continuously heatkilled algae. The dead algae rapidly released most of their phosphorus as SRP. In the batch experiments bacteria acted as consumers of the released algal phosphorus. This phosphorus uptake was dependent on the C:P ratio of the algae. During the death phase of the bacteria most of the bacterial phosphorus itself was released. The continuous supply of energy in form of dead algae in the chemostat experiments prevented the death phase of the bacteria and thus any net regeneration of phosphorus. The influence of the C:P stoichiometry of algae and bacteria on the regeneration of algal phosphorus is discussed.     

An experimental investigation of conformational fluctuations in proteins G and L

The B1 domains of streptococcal proteins G and L are structurally similar, but they have different sequences and they fold differently. We have measured their NMR spectra at variable temperature using a range of concentrations of denaturant. Many residues have curved amide proton temperature dependence, indicating that they significantly populate alternative, locally unfolded conformations. The results, therefore, provide a view of the locations of low-lying, locally unfolded conformations. They indicate approximately 4-6 local minima for each protein, all within ca. 2.5 kcal/mol of the native state, implying a locally rough energy landscape. Comparison with folding data for these proteins shows that folding involves most molecules traversing a similar path, once a transition state containing a beta hairpin has been formed, thereby defining a well-populated pathway down the folding funnel. The hairpin that directs the folding pathway differs for the two proteins and remains the most stable part of the folded protein.     

An investigation of arterial insufficiency in rat hindlimb. An enzymic, mitochondrial and histological study.

A membrane-bound aminopeptidase able to remove methionine from haemoglobin nascent peptides is described. The enzyme also hydrolyses methionine from methionyl-lysyl-bradykinin but not lysine from lysyl-bradykinin. The tripeptide Met-Ala-Ser is poorly hydrolysed. This aminopeptidase also splits amino acid 2-naphthylamides, being, however, less specific with respect to these synthetic substrates.