Competition and stability in plant mixtures in the presence of disease.

A deterministic mathematical model is developed for competition between two plant species (or genotypes) in the presence of a host-specific pathogen capable of attacking one of the species only. The complexity of the plant-plant-pathogen interaction precluded precise mathematical description of all possible long-term outcomes. However, extensive computer simulation shows that stability is not an inevitable consequence of the differential interaction, rather, the outcome depends greatly upon the growth rates and relative competitive abilities of the plant species and on the transmission efficiency of the pathogen and its effect on individual host plants. The model confirmed the general validity of previous intuitive arguments but clearly indicated that the occurrence of inflected yield curves is not a sufficient indication in itself of long-term stability.

Hinged cast and roller traction for fractured femur. A system of treatment for the Third World.

Hinged casts and roller traction were used in two developing countries to treat fractured femora, most of which were due to road traffic accidents or civil violence. This method of treatment, developed by Neufeld, is particularly useful in the Third World because it uses local materials, adapted in a hospital workshop, and circumvents the difficulties and complications of standard traction and of operative treatment. The results are reported from 11 patients treated in Uganda in 1979 and from 110 treated in the Dominican Republic in 1981 and 1982. All but one fracture united without complication or significant shortening after a brief period in hospital. The method was easily taught to hospital staff and is strongly recommended.

A threshold theorem for the general epidemic in discrete time.

A theorem, analogous to the continuous time Threshold Theorem of Kermack and McKendrick, is proved for a certain discrete time epidemic model. This model, in contrast to its continuous time analogue, leads to some solutions in which the total population of susceptibles may become infected in a finite time.

Normal processes and restraints in wound healing.

Wound healing normally follows an uninterrupted course but, for the purposes of description, it can be considered in four phases -- hemostasis, acute inflammation, repair and consolidation. Arrest of healing may occur at any phase and lead to a number of clinical problems. Repair cannot begin until the phase of acute inflammation has begun to subside; this fact is of special importance in clinical surgery. Wound healing in gastrointestinal tract and abdominal incisions is emphasized because healing problems are common in these areas and failure to heal results in morbidity and a regrettable mortality.

Authoritative parenting, child competencies, and initiation of cigarette smoking.

School-based social influence programs to prevent adolescent smoking are having limited success in the long term. Intervening earlier in the process of smoking onset, during the childhood years, may be required to prevent adolescent smoking. Child socialization variables, specifically parenting behaviors and child competencies, may be important to understanding the earliest phase of smoking onset. This study tested hypotheses of association between authoritative parenting behaviors, enhanced child competencies, and relatively low rates of initiation of cigarette smoking. Analyzing cross-sectional survey data from 937 students in Grades 3 to 8, we found general support for the study hypotheses: Authoritative parenting was positively associated with child competencies; children's competency levels were inversely related to their rates of smoking intention, initiation, and experimentation; authoritative parenting was inversely related to rates of child smoking intention and behaviors; and authoritative parenting and parent smoking status had independent associations with child initiation of cigarette smoking. These results indicate that child socialization variables merit further investigation for their potential role in the development of early intervention programs for smoking prevention.

DNA end labeling (TUNEL) in Huntington's disease and other neuropathological conditions.

Deoxyribonucleic acid of cells undergoing apoptosis is cleaved by a calcium-dependent endonuclease into oligonucleosomal-sized fragments. These fragments can be labeled using the enzyme terminal deoxynucleotidyl transferase so that the cells can be visualized immunohistochemically. Few investigators have evaluated this method in disease processes of the human central nervous system. The Tdt-mediated dUTP-biotin nick end labeling (TUNEL) technique has been investigated in preliminary studies of a variety of pathologic conditions of the human brain (e.g., gliomas, traumatic brain injury, Parkinson's disease, Parkinson's-Alzheimer's complex, multisystem atrophy, striatonigral degeneration). We focus, however, on Huntington's disease (HD) because of the availability of well-characterized pathological stages for study, and also because of the neurodegenerative diseases studied to date, only Huntington's disease revealed significant and consistent labeling with this method. This implies a possibly unique nature to the mechanism of cell death in Huntington's disease compared to the other neurodegenerative diseases studied. TUNEL+ neurons were found in Grade 1-4 HD neostriatum, while labeled astrocytes were found predominantly in the Grade 1 and 2 cases studied to date. TUNEL+ cells were also found in glioblastoma multiforme and traumatic brain injury. We conclude that while there appear to be several limitations associated with this technique, it may be useful for identifying both apoptosis and necrosis in certain neuropathological conditions.