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International Comparisons of Medical Care

In the planning of health-care systems it would be useful to know if there are universal patterns in their use. Such patterns are sought in a survey of health care in 12 areas of seven countries

By Kerr L. White

Giant Radio Galaxies

A powerful radio telescope in the Netherlands has revealed that energetic radio sources associated with galaxies are the largest obj ects known in the universe, extending millions of light-years

By Richard G. Strom, George K. Miley and Jan Oort

How Bacteria Swim

The helical filaments of the thin flagella that propel bacteria do not wave or beat but instead rotate rigidly like propellers! And they are driven by a reversible rotary motor at their base

By Howard C. Berg

The Causes of Biological Diversity

Within a single species individuals differ in many genetic traits, such as the chemical composition of their proteins. It appears that this diversity is actively maintained by natural selection

By Bryan Clarke

The Perception of Surface Color

Colors are normally regarded in terms of wavelength and intensity. The colors of surfaces are much more complex. Consider the subtle variations of color in a blue scarf carelessly thrown on a table

By Jacob Beck

The Floor of the Mid-Atlantic Rift

Last summer U.S. and French submersibles explored a rugged area at some 8,400 feet where lava wells up and the ocean floor moves outward, bearing with it the continents to the east and the west

By J. R. Heirtzler and W. B. Bryan

A Pre-Columbian Urban Center on the Mississippi

About A.D. 1000 there arose In the area north and south of what is now St. Louis the most populous Indian settlements north of Mexico. Foremost among them was Cahokia, which included some 120 mounds

By Melvin L. Fowler

The Stellar-Orientation System of a Migratory Bird

When the indigo bunting is put in a planetarium, it exhibits an ability to orient itself by the stars. This, howerer, can be only one of the cues it uses for long-distance narigation

By Stephen T. Emlen

Departments

  • 50 and 100 Years Ago, August 1975

  • Science and the Citizen, August 1975

  • Letters

    Letters to the Editors, August 1975

  • Recommended

    Books, August 1975

  • Mathematical Recreation

    Mathematical Games, August 1975

  • Amateur Scientist

    The Amateur Scientist, August 1975

  • Departments

    The Authors, August 1975

  • Bibliography, August 1975

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August 1975