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Features

The Delivery of Medical Care in China

The main feature of the Chinese system is an integrated network of neighborhood stations that serve the functions of preventive medicine, primary medical care and referral to larger centers

By Victor W. Sidel and Ruth Sidel

Integrated Optics

Tiny lasers, lenses, prisms and switches made of thin films can manipulate light to serve the same purposes as the manipulation of electrons in the thin-film devices of integrated electronics

By P. K. Tien

The Embryo As a Transplant

Pregnancy can be regarded as a graft-host relationship, like that established by an organ transplant. It is an unusual one in that the embryo seems to be indifferent to the maternal immune response

By R. E. Billingham and Alan E. Beer

Wood Pulp

This major commodity consists of wood fibers separated mechanically, thermally or chemically. It is mainly used to make paper, but it is also the source of such chemical products as rayon and acetate film

By F. Keith Hall

The Center of the Galaxy

Coded in the radio, infrared and X-ray emissions from the invisible nucleus of our galaxy is mounting evidence that It is periodically the scene of titanic explosions

By R. H. Sanders and G. T. Wrixon

Plate Tectonics and the History of Life in the Oceans

The breakup of the ancient supercontinent of Pangaea triggered a long-term evolutionary trend that has led to the unprecedented variety of the present biosphere

By James W. Valentine and Eldridge M. Moores

The Perception of Transparency

Certain mosaics of opaque colors and shapes give rise to the impression of transparency. A simple theoretical model predicts the conditions under which perceptual transparency will occur

By Fabio Metelli

The Biological Control of Dung

When native Australian dung beetles cannot cope with the large, moist dung pads of cattle, dung covers pastureland and breeds insect pests. Now foreign beetles are being imported to help out

By D. F. Waterhouse

Departments

  • 50 and 100 Years Ago, April 1974

  • Science and the Citizen, April 1974

  • Letters

    Letters to the Editors, April 1974

  • Recommended

    Books, April 1974

  • Mathematical Recreation

    Mathematical Games, April 1974

  • Amateur Scientist

    The Amateur Scientist, April 1974

  • Departments

    The Authors, April 1974

  • Bibliography, April 1974

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