Scientific American Magazine Vol 230 Issue 4

Scientific American Magazine

Volume 230, Issue 4

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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

Victor W. Sidel, 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

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

R. E. Billingham, 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

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

R. H. Sanders, 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

James W. Valentine, 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

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

D. F. Waterhouse

Departments

Letters to the Editors, April 1974

50 and 100 Years Ago, April 1974

The Authors, April 1974

Science and the Citizen, April 1974

Mathematical Games, April 1974

The Amateur Scientist, April 1974

Books, April 1974

Bibliography, April 1974