Chest physiotherapy in primary pneumonia.

One hundred and seventy one patients with primary pneumonia entered a single blind, placebo controlled trial of physiotherapy. Treatment was allocated at random, physiotherapy consisting of postural drainage, external help with breathing, percussion, and vibration and the controls receiving advice on expectoration, deep breathing, and how to exercise to avoid thrombosis. Principles of pharmaceutical management were the same in the two groups. There was no objective evidence that daily physiotherapy helped during the acute phase of the disease. On the contrary, in younger patients, smokers, and patients with interstitial pneumonia physiotherapy appeared to prolong the duration of fever as well as the hospital stay. It is concluded that chest physiotherapy is at best useless in patients with primary infectious pneumonia.     

Repetitive sequences of the sea urchin genome: Distribution of members of specific repetitive families

Three repetitive sequence families from the sea urchin genome were studied, each defined by homology with a specific cloned probe one to a few hundred nucleotides long. Recombinant λ-sea urchin DNA libraries were screened with these probes, and individual recombinants were selected that include genomic members of these families. Restriction mapping, gel blot, and kinetic analyses were carried out to determine the organization of each repeat family. Sequence elements belonging to the first of the three repeat families were found to be embedded in longer repeat sequences. These repeat sequences frequently occur in small clusters. Members of the second repeat family are also found in a long repetitive sequence environment, but these repeats usually occur singly in any given region of the DNA. The sequences of the third repeat are only 200 to 300 nucleotides long, and are generally terminated by single copy DNA, though a few examples were found associated with other repeats. These three repeat sequence families constitute sets of homologous sequence elements that relate distant regions of the DNA.     

Low-density lipoprotein preparation by combined diafiltration and ultracentrifugation

A method for isolating low-density lipoprotein by combining diafiltration and ultracentrifugation is described. Diafiltration separates plasma components by use of an ultrafiltration membrane that excludes particles of molecular weight greater than 300,000. The retentate is concentrated three- to fourfold by ultrafiltration, allowing large-scale preparation of low-density lipoprotein. Low-density lipoprotein prepared in this manner is similar in physical, chemical, and biologic properties to low-density lipoprotein isolated by sequential density ultracentrifugation alone. When low-density lipoprotein, prepared by either method, was added to human umbilical vein endothelial cell cultures, no cytotoxicity was observed. The techniques described reduce the demand on multiple rotors and ultracentrifuges for large-scale preparation of low-density lipoprotein suitable and often needed for tissue culture studies.     

Gaucher's disease: Lack of antibody response to intravenous glucocerebrosidase

An enzyme-linked immunosorbent assay was developed to investigate antibodies produced against purified human placental glucocerebrosidase. Anti-glucocerebrosidase titers in serum from patients who were injected with the enzyme were compared with that in rabbits immunized with the same preparation. No antibodies were detected in human sera over periods of three weeks to 41 months after infusion of the enzyme.     

Effects of competition and shading in planktonic communities

A model for several algal species which compete both for light and for nutrients, and which are also subject to settling and diffusion, is considered. The settling speeds and diffusion coefficients are assumed to be small, in a sense to be made precise later, and a singular perturbation argument is used. In certain cases vertical segregation of the algal species is observed, and the mechanism for this is interpreted biologically.Supported by the Danish Natural Science Research Council (Grant No. 11-8321)     

Synchronization of the behaviour within nests of the antLeptothorax acervorum (Fabricius)—II. Modelling the phenomenon and predictions from the model

Observations on activity of ants of the speciesLeptothorax acervorum show that ants within the nest are inactive for about 72% of their time (Frankset al., 1990.Bull. math. Biol.,52, 597–612). By examination of the activity of individual ants it is demonstrated that activity bouts of individuals are highly synchronized. The bursts of activity detected by Frankset al. occurred three to four times per hour. In this paper we develop a model to describe the phenomenon. As a result of the interdependence of the number of active ants within the nest and the high level of community activity some predictions are made, which are supported by experimental data in a quantitative way. In case of starvation the number of active ants will increase and no rhythms should occur. When proportionally more brood is present the rhythms should occur with a higher frequency. Eventually the rhythm breaks down and a stable equilibrium is reached.     

Aggregation and the competitive exclusion principle

A mathematical model for aggregation in a single animal population is set up. It relies on two premises. First, there is an advantage to individuals in the population in grouping together, for example for social purposes or to reduce the risk of predation. Second, the intra-specific competition at a point depends not simply on the population density at that point but on the average population density near the point, since the animals may move to find resources. The model is then extended to competing populations, and inter-specific competition is also assumed to depend on an average population density. It is shown that the resulting aggregation may lead to the co-existence of populations one of which would otherwise be excluded by the other. This finding is discussed with regard to the Competitive Exclusion Principle.