Comparative physiology is based on the premise that animals are more or less similar and thus can be compared. This does not mean that they are alike, and a deviation from the general pattern is often as meaningful and interesting as the similarities.

The difficulty of comparing organisms of different size is symbolized in figure 45, which shows our old friend Gulliver, as Figure 45. Gulliver presented a problem of scaling, the Lilliputian emperor had to decide how much food the Man Mountain needed. (Reproduced by permission of Doubleday & Company, Inc. from Gulliver's Travels by Jonathan Swift, illustrated by Leonard Weisgard. Illustrations copyright 1954 by Nelson Doubleday, Inc.) well as a Lilliputian walking down the cobblestone street. The immediate problem that the Lilliputian emperor had to face when Gulliver arrived was how much food the Man Mountain needed. Swift (1726) reported that it was exactly 1728 Lilliputian portions. Is this estimate correct, and on what basis can we compare mammals of different size?

Those who have dissected a racehorse or a greyhound may have noted that these animals have larger than proportionate hearts. In proportion to their body size mammals generally have very similar heart size, about 5 or 6 gram per kg body weight, and we are so used to this scale that we immediately notice a deviation.