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Using a combined gradient optical trap and evanescent wave light-scattering force-measurement technique, long-range colloidal forces were measured between a single Candida albicans yeast cell and a flat, bare glass surface in electrolyte concentrations ranging from 0.1 to 100 mM NaCl. The Derjaguin−Landau−Verwey−Overbeek (DLVO) theory was compared to experimentally measured equilibrium force curves and found to provide a close approximation to the decay length of the measured forces for electrolyte concentrations up to about 0.23 mM NaCl. At higher electrolyte concentrations (≥0.5 mM NaCl), decay lengths of force curves in experimental measurements were consistently longer than Debye lengths calculated from the electrolyte concentrations. In electrolyte concentrations of 10 and 100 mM NaCl, most cells attached rapidly, which prevented measurements of long-range forces. The small fraction of cells remaining unattached in these higher electrolyte concentrations displayed purely repulsive forces. These results show that the DLVO theory accurately describes cell-surface interactions when the Debye length is in the range of 20−30 nm but underpredicts the decay length of the interactions at higher electrolyte concentrations.

Mycobacterium avium subspecies paratuberculosis, the organism responsible for paratuberculosis in cattle and sheep has been found in wild rabbits (Oryctolagus cuniculus) in the east of Scotland. Few studies have investigated either the level of faecal contamination by rabbits on farms, or the potential infectivity of rabbit excreta. The rate of rabbit faecal contamination deposited and the numbers encountered were estimated for 21 fields on 4 farms with a paratuberculosis problem. 7357±2571 S.E.M. rabbit faecal pellets were deposited per hectare per day and up to 81000 pellets/ha (‘standing crop’) were encountered in October/November 1998. Where access to rabbits was restricted, the standing crop of faeces encountered fell to 22000 pellets/ha. The prevalence of infection with M. a. paratuberculosis was assessed for 83 rabbits from the four farms. M. a. paratuberculosis was isolated from rabbits on all farms with an overall prevalence of 17%. Out of 17 rabbits from which urine was available, M. a. paratuberculosis was isolated from two – the first reported isolation from urine in wild rabbits. The mean number of colony-forming units per gram of infected rabbit faeces was 7·6×105±5·2×105. A relative estimate of the input of M. a. paratuberculosis onto pasture, at the stocking levels found on the four farms, showed that sheep and cattle potentially contributed 4 and 125 times more organisms/ha per day respectively than rabbits. However, rabbits could still contribute millions of M. a. paratuberculosis organisms per ha per day. Existing rabbit control measures on farms may be inadequate in reducing the risk of transmission to livestock.

ABSTRACTThe role of wildlife species in the epidemiology of paratuberculosis has been the subject of increased research efforts following the discovery of natural paratuberculosis in free-living rabbits from farms in east Scotland. This paper describes the experimental inoculation of young calves with an isolate ofMycobacterium aviumsubsp. paratuberculosisrecovered from a free-living rabbit. After a 6-month incubation period, all eight calves inoculated with the rabbit isolate had developed histopathological and/or microbiological evidence of M. aviumsubsp. paratuberculosisinfection. Similar results were obtained from a group of calves infected with a bovine isolate of M. aviumsubsp. paratuberculosis. The virulence of the rabbit isolate for calves demonstrated in this study suggests that rabbits are capable of passing paratuberculosis to domestic ruminants and that wildlife reservoirs of M. aviumsubsp. paratuberculosisshould therefore be considered when formulating control plans for the disease.

ABSTRACTRecent reports of natural paratuberculosis (or Johne's disease) in rabbits, foxes, and stoats has focused debate on the presence and importance of wildlife reservoirs in the epidemiology of this disease. This paper describes an extensive study investigating 18 nonruminant wildlife species for evidence of paratuberculosis. Using both culture and histopathological analysis, fox, stoat, weasel, crow, rook, jackdaw, rat, wood mouse, hare, and badger were found to harborMycobacterium aviumsubsp. paratuberculosis, the causative organism of paratuberculosis, suggesting that the epidemiology of this disease is more complex than previously realized.

Various strategies aimed at improving IgG1 antibody accumulation in transgenic tobacco cell and organ cultures were tested. The form of tissue had a significant effect on antibody levels; shooty teratomas were less productive than hairy roots or suspended cells. Although there were several disadvantages associated with hairy roots compared with suspensions, such as slower growth, slower antibody production, and formation of a greater number of antibody fragments, the roots exhibited superior long-term culture stability. Antibody accumulation in hairy root cultures was improved by increasing the dissolved oxygen tension to 150% air saturation, indicating the need for effective oxygen transfer in root reactors used for antibody production. Preventing N-linked glycosylation using tunicamycin or inhibition of subsequent glycan processing by castanospermine reduced antibody accumulation in the biomass and/or medium in cell suspensions. Loss of antibody from the cultures after its secretion and release into the medium was identified as a major problem. This effect was minimized by inhibiting protein transport in the secretory pathway using Brefeldin A, resulting in antibody accumulation levels up to 2.7 times those in untreated cells. Strategies for protecting secreted antibody, such as addition of poly(vinylpyrrolidone) and periodic harvesting from the medium using hydroxyapatite resin, also increased antibody titers. The mechanisms responsible for the disappearance of antibody from plant culture media were not clearly identified; degradation by proteases and conformational modification of the antibody, such as formation of aggregates, provided an explanation for some but not all the phenomena observed. This work demonstrates that the manipulation and control of culture conditions and metabolic processes in plant tissue cultures can be used to improve the production of foreign proteins. However, loss of secreted antibody from plant culture medium is a significant problem that may limit the feasibility of using product recovery from the medium to reduce downstream processing costs relative to agricultural systems.

Abstract: Marked changes in brain monoamine content and NPY content occur during maturation and ageing. Earlier in vivo studies in our laboratory have reported blunted K+ stimulated noradrenaline release and reduced NPY overflow in aged animals using microdialysis and push pull techniques. In this study, in vitro superfusion techniques were established to measure endogenous noradrenaline, NPY, DOPAC and 5-HIAA overflow from the hypothalamus of 1, 5 and 16 month old Sprague-Dawley rats. A period of high K+ (56 mM) stimulation was carried out to elicit maximal release. Basal noradrenaline overflow was similar in all age groups of rats and during K+-induced depolarisation similar 3–4 fold increases were observed. On the other hand, basal and K+ stimulated NPY overflow were significantly greater in the adult rats compared to 1 month and 16 month old rats. Despite differences in absolute NPY overflow, the relative increase over resting was not significantly different across age groups. The molar quantities of hypothalamic NPY overflow at rest and under K+ stimulated conditions were three orders of magnitude lower than noradrenaline. Results of these studies suggest that both NPY and noradrenaline can be released from a similar hypothalamic pool. Basal and K+-evoked DOPAC and 5-HIAA overflow were similar between the 3 age groups. Thus the overflow of hypothalamic noradrenaline, DOPAC and 5-HIAA under in vitro conditions was not altered from 1 to 16 months. In contrast, 5 month old rats had significantly higher NPY overflow than the other age groups (P < 0.05), consistent with a reported decline in NPY content with advanced age. Hypothalamic noradrenaline overflow was not affected by ageing, suggesting that a selective loss of NPY in the arcuo-PVN projection, or other projections to the hypothalamus with ageing may contribute to the reduction in NPY overflow in aged rats.

An experimental model of pneumonic pasteurellosis in sheep was used to investigate the role of serum antibody in resistance to this disease. Lambs which had been vaccinated with a sodium salicylate extract of Pasteurella haemolytica type A1 were protected against challenge with PI3 virus followed by P. haemolytica type A1 7 days later. The majority of untreated lambs and lambs which had received either 200 ml of antiserum to P. haemolytica or 200 ml of control serum intraperitoneally 18 h before infection with P. haemolytica type A1 succumbed to the challenge. Lymphocytes from vaccinated lambs showed a specific proliferative response when exposed to P. haemolytica type A1 sodium salicylate extract, and this response increased after exposure of these animals to P. haemolytica type A1 in aerosol. The results indicate that the humoral immune response alone is incapable of affording protection against experimental pasteurellosis and that cell-mediated immunity may play an important part in resistance to this disease.

Summary Jaagsiekte, a contagious lung tumour of sheep, was induced within 3–6 weeks in day-old lambs by intratracheal inoculation of SPA lung fluids concentrated by centrifugation. Electronmicroscopic examination of the tumour revealed retrovirus particles whose morphogenesis and morphology support biophysical and immunological findings that suggest a relationship with type B and type D retroviruses.

Summary In two experiments, 18 specific-pathogen free (SPF) lambs were inoculated by several routes with the Scottish strain of caprine herpesvirus 1 (CHV1). Seventeen of the lambs developed interstitial changes in the lungs ranging from focal cellular infiltration to a widespread proliferative pneumonia.

Sheep pulmonary adenomatosis ([SPA] ovine pulmonary carcinoma) is a transmissible lung cancer of sheep that has been associated etiologically with a type D- and B-related retrovirus (jaagsiekte retrovirus (JSRV]). To date it has been impossible to cultivate JSRV in vitro and therefore to demonstrate the etiology of SPA by a classical approach. In addition, the presence of 15 to 20 copies of endogenous JSRV-related sequences (enJSRV) has hampered studies at the molecular level. The aim of this study was to investigate whether the expression of exogenous JSRV was specifically associated with neoplasia in SPA-affected animals. Initially, we found that enJSRVs were transcribed in a wide variety of normal sheep tissues. Then, by sequencing part of the gag gene of enJSRV we established a ScaI restriction site in gag as a molecular marker for the exogenous form of JSRV. Restriction enzyme digestion of PCR products obtained from the amplification of cDNA from a total of 65 tissues collected from SPA-affected and unaffected control sheep revealed that the exogenous form of JSRV was exclusively and consistently present in tumor tissues and lung secretions of the affected animals. In addition, exogenous JSRV provirus was detected only in DNA from SPA tumors and not from nontumor tissues of the same animals. This study has demonstrated clearly that the exogenous form of JSRV is specifically associated with SPA tumors.

This paper identifies the need for a new range of end effectors suitable for non-rigid products and introduces a novel non-contact gripping device. The end effector operates on the principle of generating a high-speed flow between the end effector and product surface thereby creating a vacuum which levitates the product. The lifting forces and conditions are theoretically discussed. The experimental results are presented using the end effector that has been operated to lift non-rigid food materials such as jelly blocks.

A type D-related retrovirus has been demonstrated in enzootic nasal tumors (ENTs) of sheep and goats. This retrovirus, ENT virus (ENTV), has antigenic cross-reactivity with the jaagsiekte sheep retrovirus (JSRV), which is associated with a contagious lung tumor of sheep (sheep pulmonary adenomatosis). Here, we present the first report of nucleic acid sequence from ENTV which confirms, at the nucleic acid level, that this retrovirus is related to JSRV yet apparently distinct from it. Reverse transcription-PCR followed by restriction enzyme digestion specifically identified ENTV. By this technique, ENTV was demonstrated exclusively in tumor tissues and exudates of animals with ENT. Thus, there is a unique and consistent association between ENT and the retrovirus, just as there is between JSRV and sheep pulmonary adenomatosis. This gives further weight to the hypothesis that these retroviruses are the etiologic agents of the tumors.

Ovine pulmonary carcinoma (OPC) is a contagious lung cancer of sheep that is presumed to be caused by an exogenous retrovirus of sheep, jaagsiekte sheep retrovirus (JSRV). The sheep genome carries 15 to 20 copies of endogenous sheep retrovirus (ESRV) loci that hybridize to JSRV DNA probes. In order to clarity the etiologic roles of ESRV and an exogenous JSRV-like retrovirus (exJSRV) in OPC, we assessed sequence differences between ESRV and JSRV. Molecular characterization of six ESRV loci revealed restriction sites specific for JSRV. Nucleotide sequences of ESRVs from sheep of different breeds were similar to those of JSRV in structural genes but divergent in U3. Therefore, primers specific for the U3 sequences of exJSRV were designed for use in the PCR. Of 13 tumor DNAs tested by PCR with these exogenous-virus U3 primers, 8 produced DNA fragments that hybridized with the JSRV gag probe, but neither lung DNAs from healthy sheep nor DNAs from nontumor tissues of diseased sheep produced similar DNA fragments. exJSRV PCR products from tumor DNAs of sheep with OPC from three continents had restriction profiles similar to each other but different from those of ESRVs upon digestion with EcoRI, HindIII, NdeI, KpnI, and ScaI. These exjSRVs could be classified into two genotypes according to U3 sequences and restriction profiles. U3 sequences of exJSRV proviruses in tumors strongly resembled those of JSRV but differed from those of ESRVs, suggesting that exJSRVs, rather than ESRVs, are primarily associated with oncogenesis in OPC.

The majority of textile fabrics are either woven or knitted. Knitted fabrics are most frequently produced on weft knitting machines. The range of machinery is very diverse but the same basic mechanism is employed to convert textile yarn into knitted textile fabric. The mechanism is a specialized needle and cam system known as a latch needle cam system. This paper develops a general model for the mechanical forces that arise in normal operation of a latch needle cam system. The limitations of previous models are noted. The model may be used to predict mechanical forces for any specified cam profile and for the most common needle and cam arrangements. The model will be used in a following paper on yarn forces in latch needle cam systems. The performance of the model will be reported in a following paper describing an experimental programme and experimental results

An optimization strategy is developed to improve the performance of strain gauge transducers. For a specific transducer configuration, the method used is to select an output characteristic to be optimized and to set realistic constraints on the remaining output characteristics and on physical dimensions. Using this strategy, a non-linearly constrained optimization problem may be formulated mathematically.Numerical methods to solve problems of this type are discussed and practical details arising from their use are considered. Correctly formulated problems are solvable quickly and efficiently with routines which are generally available.The techniques introduced here are applicable to a wide range of design problems in transducers of this type and provide a significant design aid.

A survey of wild rabbits in Tayside, Scotland revealed that 67 per cent were infected with Mycobacterium aviumsubspecies paratuberculosis. In general, the infected rabbits had histopathological changes within the lymph nodes and intestines which were consistent with the changes due to paratuberculosis in ruminants. The survey raises the possibility that rabbits and other wildlife may be involved in the epidemiology of paratuberculosis, a possibility which has important implications for the control of the disease.

Molecules stream in collisionless flow out of a reservoir into an axially symmetric tube consisting of two equal and oppositely inclined conical frustra—a shape used in industrial vacuum traps. In the general case there is a baffle in the centre of the tube. Some of the molecules strike the wall of the tube, some the baffle, and are reflected; eventually they either fly back into the reservoir or escape out of the tube into the vacuum beyond. Other particles stream directly from the reservoir into the vacuum without any collisions with a surface. The impact density of molecules along the wall in the steady state is determined by a system of integral equations, four in all when the baffle is present, otherwise two. These numbers can be reduced by half by utilizing certain combinations of the equations, suggested by the physical system, that yield analytical relations between the impact densities. The remaining integral equations are solved numerically. One of the kernels has an indeterminacy corresponding to the kink in the longitudinal cross-section of the tube, but the existence and uniqueness of the solution is established by analytical means. The results of calculations of the molecular impact density on the surfaces and the conductance of the tube with baffle for a number of typical systems are given in graphical form.