Dimensions of Animals and their Muscular Dynamics

Abstract

ON November 4 Prof. A. V. Hill gave a Friday Evening Discourse at the Royal Institution, his subject being "The Dimensions of Animals and their Muscular Dynamics". He pointed out that mammals vary in size in the ratio of 40,000,000 : 1, from 4–5 grams to 150 tons. In general, a small animal carries out each movement more quickly than a large animal, its muscles having a higher 'intrinsic speed' and being able, in proportion to their size, to develop more power. In a group of 'similar' animals there is an evident tendency for the maximum speed, and the height and length of jump, to be independent of size. This depends upon a variety of limiting factors, particularly the mechanical strength of the structure of the animals, and the oxygen supply to their muscles. In the cetaceans, from porpoises to whales, the maximum speed that can be maintained (about 15 knots) is much the same in spite of a 5,000 fold variation of weight. A calculation of the drag due to skin friction shows that the power required to overcome it would be impossibly high if turbulence occurred over more than a small fraction of the surface.