... strain upon the heart in moderate degree, such as running, working, and thinking, are not only not harmful, but beneficial to it, increasing both its strength and its size. The heart, for instance, of a thoroughbred race-horse is nearly twice the size, in proportion to his body weight, of the heart of a dray-horse or cart-horse; and a deer has more than twice as large a heart as a sheep of the ... — A Handbook of Health • Woods Hutchinson
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