Schack August Steenberg Krogh (November 15, 1874 - September 13, 1949) was a Danish zoophysiologist and pioneer in comparative studies on animals. He contributed a number of fundamental discoveries within several fields of physiology, and is famous for developing the Krogh Principle (which states that for such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied). In 1910 he founded the first laboratory for animal physiology (zoophysiology) at the University of Copenhagen. Much of his work was carried out in collaboration with his wife, Marie Krogh (1874-1943), a renowned scientist in her own right. In 1920 August Krogh was awarded the Nobel Prize in Physiology or Medicine for the discovery of the mechanism of regulation of the capillaries in skeletal muscle. He was first to describe the adaptation of blood perfusion in muscle and other organs according to demands through opening and closing the arterioles and capillaries. He died in 1949 at the age of 74.