Search

The orientation of repeating units in chromosomal ribosomal DNA of Xenopus was determined by denaturation mapping in order to test a model for gene rectification. The model postulates an alternating orientation that will allow the formation of pallindromic loops between adjacent repeats. Mutations would then be lost or driven to fixation by random correction of one sequence by another, following genetic homogeneity among the repeats. Head-to-tail orientation was found, ruling out the model for this system.

A series of nine dimensions of 536 shoulder girdles in 41 genera of primates had previously been studied as reflecting function within locomotion in that anatomical region. Their combined examination by canonical analysis and neighborhood limited classification suggests that not only do the two methods give results which are consonant with one another but also that both have their separate parts to play in the description of relationships between biological objects. Both methods imply that underlying the many variations in shape of the shoulder girdle in primates are a small number of functional factors presumably related to phenomena of a genetic, developmental or evolutionary nature.

1. 1.|A comparison has been made between the swinging-buckets rotor and the fixed-angle rotor for density-labelling experiments. 2. 2.|The enzymes examined were β-galactosidase (β- d -galactoside galactohydrolase, EC 3.2.1.23), l -phenylalanine ammonia-lyase (EC 4.3.1.5) and acid phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.2); it was found that the fixed-angle rotor offered greater separation and resolution and shorter equilibration times compared with the swinging-buckets rotor at the same angular velocity. 3. 3.|By exploiting the greater flexibility offered by the fixed-angle rotor it is possible to obtain either a 6-fold improvement in separation or a 6-fold reduction in equilibration time. The significance of these results for density-labelling work is discussed.

The authors used statistical methods to interpret 1,430 values of 24-hour urinary estriol. This determination is valuable in the last three months of pregnancy if values lower than 10 mg/24-hour are obtained at the 40th week, the tests must be repeated and additional examinations should be made to determine the condition of the fetus. This test is invaluable in the surveillance of cases of toxaemia of pregnancy, threatened premature births, severe forms of Rhesus incompatibility, and in cases of fetal death. This study showed that the prognosis is grave when reduced or flattened oscillations of the trace of fetal cardiac frequency are associated with very low levels of estriol.

A previous study on assignment of four major categories of psychotropic drugs to psychiatric inpatients generated the hypothesis that patients assigned minor tranquilizers consisted of two distinct sub-groups, one of which consisted of diagnosed alcoholics. The present study confirmed that hypothesis. More importantly, it found that minor tranquilizer assignment to non-alcoholic inpatients was a virtually random procedure. The general ability of predicting psychotropic drug assignment via a statistical model was nevertheless supported.

Two statistical experimental designs were used to investigate factors involved in 90-day mortality from secondary disease in lethally irradiated mice treated with rat bone marrow. Secondary disease is a graft-versus-host syndrome that has a mortality of about 65-95% in this transplant situation. When the factors--age-of-donor-cells, day-of-cell-injection, dose-of-marrow-cells, sex, and environment--were examined for their main effects and interactions, some combinations of these factors were found to give about 25% 90-day mortality. The experiments indicate that the lowest mortality can be achieved with an injection of 40 million or more cells 1 day after irradiation and an ultraclean environment of unlimited filter-top caging.

Estimates are presented of the transition probabilities and transition times from dysplasia to carcinoma in situ of the uterine cervix based on a statistical model of the natural history of this disease. The estimates, obtained from a longitudinal study of 557 women, were contrasted with prevalence rates obtained in a self-selected sample of over 11,000 women from Barbados, West Indies. These two independent sets of estimates, based on two different experimental designs, were shown to be concordant. The formula for the computation of the standard deviation of these estimates was given, together with the results of this computation for the observed sample data. The effects of those covariables that have been associated with the incidence of cervical neoplastic disease on these estimates were examined. The transition times and probabilities were associated with the total number of pregnancies but were not dependent on age at first coitus or age at first pregnancy. The results of this investigation provide an index of the history of cervical neoplastic disease that might be of use in contrasting the experience of different subsets of the population with respect to their transition probabilities and transition times through the several stages of the disease process.

In an effort to determine more accurately the physical characteristics of human tendon, stress-strain and tensile strength studies were performed on tendons removed from amputated lower limbs. The tendons of M. extensor digitorum longus, M. extensor digitorum brevis, M. extensor hallucis longus, M. flexor digitorum longus and M. flexor hallucis longus were used in the studies. Tensile strength of the extensor tendons averaged 13,392 psi while that of the flexor tendons was less, with an average of 10,944 psi. These results indicate that, of the tendons tested, the extensors are about 20 per cent stronger than the flexors. The stress-strain data were analyzed by a computerized statistical method utilizing a multiple-regression analysis employing as many as 8 variables. All stress-strain curves shown were derived by this method. The difference in stiffness previously reported to exist between embalmed flexor and extensor tendons was not manifest in the present study. However, in the range from 0 to 3·0 per cent strain, thought by many to be the normal physiologic range, extensors and flexor tendons were seen to react differently to stress. The flexors initially exhibited greater strain per unit stress and gradually became stiffer, the stress-strain curves exhibiting an upward concavity. The extensors were initially stiffer, gradually responding with more strain per unit stress, and the stress-strain curve was slightly concave downward. The stress-strain curves of unembalmed flexor and extensor tendons as calculated in the present study are reminiscent of the curves previously reported for embalmed extensor tendons.

International audience; Redundancy is a fundamental feature of biological motor systems. For example, when touching an object, many different combinations of movements of the shoulder, elbow, wrist, and finger joints result in the same movement at the fingertip. Exploiting this redundancy, the motor system distributes work across effectors to minimize signal-dependent noise and effort. When an error occurs, however, the motor system must assign the error to specific effectors, even though it may be ambiguous which effector caused them. Here, we studied the principles of responsibility assignment by using a bimanual task, in which the left and right hands jointly moved a visual cursor. We found that participants assigned errors, which were induced by visual rotation of the cursor, in a unified manner for correction and adaptation; the hand that corrected more for the error within the current movement also showed a bigger adaptive change in the next movement. Right-handed participants corrected errors more with their left hands, even though they corrected faster with their right hands in nonredundant tasks. Further experiments show that the motor system assigns responsibility preferentially to the hand that was previously exposed to larger errors. Our results show that responsibility assignment is a flexible process that attributes errors to the most likely cause.

SUMMARY-A model has been derived for the effect of the chemotherapeutic agents cyclophosphamide (CY), 5-fluorouracil (5-FU), and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) on the survival of mice bearing a transplantable lymphoma. The model is based on assumptions that 1) failures in treatment result from the survival of viable malignant cells, 2) the lymphoma cells in the host increase exponentially with time, 3) the host dies when the lymphoma cell population reaches a critical value, and 4) the number of lymphoma cells in the host decreases exponentially as a function of the infected drug dose. Parameters were found for the growth of lymphoma cells in vivo and for the survival of lymphoma cells in the host following the administration of CY, 5-FU, and BCNU. When these parameters were incorporated into the model, predictions were obtained concerning the survival time of lymphoma-bearing mice as well as the fraction of long-term survivors as a function of the injected dose. It was found that the model and experimental data were in excellent agreement for low doses of the drug, i.e., doses which reduced the survival of the lymphoma cell population to the order of 10(-4) survival. However, discrepancies were observed above these dose levels. The discrepancies are discussed in terms of the assumptions of the model.

703 standardized test specimens of dry cortical bone from different shaft regions of human femora were subjected to compression till failure parallel to the long axis of the shaft. The rate of load increase was 50 kg/cm2/sec. The significance of four sources of variation was tested, i.e. cross-sectional area (site), quadrant (position), side of the body, and individual, in three analyses of variance. All main effects and the interactions site x position, site x individual, position x individual, body side x individual are significant. A constant pattern of strength distribution in the proximal three cross-sectional areas is shown: this pattern is changed in the two distal cross-sectional areas, but it is the same on the left and right sides of the body apart from variations by the main effects. The pattern of strength distribution in the two distal cross-sectional areas probably changes with age. The distributions of mean compressive strength of femur shafts from two age groups are presented diagrammatically in Fig. 1, and the respective means are given in Fig. 2.