Additionally, we can compress and expand the lungs by muscles in the chest and thus force air in and out of the lungs. Support of terrestrial animals by legs. Suppose that we scaled up an insect by a factor of 100. If the tissue and exoskeleton were exactly of the same composition, and thus density, the larger insect would weigh one million times as much as the original. But, the weight of the body would be supported on legs with only 10,000 times as much cross sectional area, and thus total strength, as the original.
Force divided by area over which the force is applied is called pressure.
Well, like our nutrition problem, we can change construction methods and materials . And, we can change proportions of the body plan , in this case by making the leg thicker relative to the body size as the animal becomes larger. Notice that for the smaller animals, D'Arcy Thompson pairs a mammal with a bird, showing that while the principle holds for two different groups of animals. It would have been nice if Thompson had given us data for a large bird, such as an ostrich or a very large mammal, such as an elephant, which has very large diameter legs, relative to its body size. Notice that the principle of proportionally larger diameter supporting structures for larger animals also applies to plants.