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101.
M J McLaren D M Hawkins H J Koornhof K R Bloom D M Bramwell-Jones E Cohen G E Gale K Kanarek A S Lachman J B Lakier W A Pocock J B Barlow 《BMJ (Clinical research ed.)》1975,3(5981):474-478
A survey to determine the prevalence of rheumatic heart disease (R.H.D.) in Black children was conducted in the creeches and primary schools of the South Western Townships of Johannesburg (Soweto). A total of 12 050 Black children were examined by 10 cardiologists in May to October 1972. The overal prevalence rate of R.H.D. was 6.9 per 1000, with a peak rate of 19.2 per 1000 in children of the seventh school grade. The maximal age incidence was 15-18 years and there was a female preponderance of 1 6:1. A rise in prevalence occurred with increasing family size. Most children (92%) were asymptomatic, and in 82.5% R.H.D. was diagnosed for the first time during the school survey. The commonest valve lesion was mitral regurgitation, which was present in 93% and occurred as an isolated lesion in 47.5%. Lancefield''s group A beta-haemolytic streptococcus was isolated from the throats of 52 per 1000 Soweto children. The auscultatory features of a non-ejection systolic click and late systolic murmur were prevalent (13.9 per 1000) and had several epidemiological factors in common with R.H.D. A comprehensive preventative campaign is urgently needed in South Africa, directed at both primary and secondary prophylaxis of R.H.D. The socioeconomic status of the community must be improved if optimal prevention is to be achieved. 相似文献
102.
The entry of labelled calf-thymus histone, lysozyme, and poly-L-lysine into barley root tips was studied at concentrations which strongly inhibit root elongation. The macromolecules were suitably labelled and at these concentrations it was found, by autoradiography and fluorescence microscopy, that histone and lysozyme readily entered the roots and appeared to bind mainly to cell walls of the epidermis and cortex and to penetrate the cytoplasm occasionally. Except in cap cells, nuclei were rarely penetrated. Poly-L-lysine readily permeated cell walls and invaded cytoplasm and nuclei throughout the root tip. Some cells were damaged by contact with basic macromolecules, as evidenced by a change in appearance of protoplasts under phase contrast and by the inability of these same protoplasts to exclude labelled β-lactoglobulin. Such damage was restricted to cells in contact with the outer solution. Interior to the epidermis, development of many cells was inhibited without visible signs of damage. Evidence supports the conclusion that in the presence of polybasic polymers the integrity of cell membranes is altered, thereby allowing leakage of some cell constituents essential for normal development. 相似文献
103.
Summary A naturally occurring, cross-linked fraction, constituting about 1% of the total DNA, has been isolated from the DNA of mice and rats. In sharp contrast to the rest of the rapidly renaturing DNA, this material shows poor binding ability during incubation in agar with DNA of the same species. 相似文献
104.
Effect of various procedures on the viability of mouse embryos containing half the normal number of blastomeres 总被引:1,自引:0,他引:1
Half embryos produced from 8-cell or compacted stages were cultured in vitro for 1-2 days and transferred to oviducts or uteri of recipients at different stages of pseudopregnancy. The proportion of live fetuses was low (8-12%), except for one group (27%) in which half embryos were cultured in vitro for 1 day and transferred into oviducts on the 1st day of pregnancy. Monozygotic twin production rate, however, was low (1 out of 10) even in this group. Fetal weight on the 18th day of gestation was significantly lower after transfer of half embryos than after transfer of similarly treated but undivided embryos. Half embryos produced from the 2-cell stage were inserted into empty zonae, embedded in agar, cultured in ligated mouse oviducts for 2-4 days and transferred to oviducts of recipient females on the 1st day of pregnancy or pseudopregnancy. When twin embryos cultured for 2-3 days were transferred to pseudopregnant recipients together with control embryos, 4 sets of monozygotic twins and 5 singletons out of 10 sets of twin embryos were obtained on Days 18-19 of gestation, giving a survival rate of 65%. 相似文献
105.
106.
Summary In order to study any Conformational changes associated with ultraviolet irradiation of TMV-RNA, methods of circular dichroism and absorbance-temperature profile were applied. RNA irradiated in water at 254 nm showed a distinct change in CD spectrum, but there was only a slight change accompanying irradiation in phosphate buffer.A small change in absorbance-temperature profile at 258 nm is associated with irradiation of RNA in water; RNA irradiated in phosphate buffer and Mg++ solutions showed essentially no changes.It is concluded that conformational changes accompanying irradiation of RNA in water are greater than those taking place in phosphate or magnesium solutions, and the enhanced change in water is related to the larger quantum yield for inactivation found in water than in buffer solutions.Photochemistry of Macromolecules XXXIII, supported in part by the U.S. Atomic Energy Commission, contract AT(11-1)-34, Project 116. 相似文献
107.
Ian A. McLaren 《The Journal of general physiology》1965,48(6):1071-1079
Bělehrádek's temperature function in which metabolic rate V is related to temperature T by 相似文献
108.
109.
110.
The kinetics and cytidine 5-triphosphate (CTP) feedback inhibition of CTP synthetase in wild-type and four mutants of Chinese hamster V79 cells have been studied. The enzymes of the wild type and three of the four mutants exhibited positive cooperativity with the substrate uridine 5-triphosphate (UTP). Three of the mutants had K
m app and S
50 valuves distinctly greater than those of the wild type, while the fourth mutant had values similar to those of the wild type. all four mutants exhibited resistance to CTP feedback inhibition, while the wild type was sensitive to such inhibition. It is postulated that a single mutational event in each mutant had caused a concomitant change of the enzyme in its binding both to the substrate UTP and to the end-product CTP.This work was supported by Grant GM 20608 from the U.S. Public Health Service. 相似文献