'39. The heels of the shoe should be about one-third the substance of the toe.
'40. This form of shoe is preferred to a high heel, as it allows the frog to perform its function, by embracing the ground, and acting as a spring.
'41. The weight of the shoe being diminished at the heel, the labour of the muscles that bend and extend the leg is diminished.
'42. Where no part of the crust can be removed from the toe, and the horse has been in the habit of wearing high shoes, the heels should be made only one-tenth of an inch, every time of shoeing, thinner than the shoes removed.
'43. If the frog be callous and sound, and the toe admits of being shortened, the iron may be diminished at the heels, in the same proportion as the toe is shortened.
'44. The muscles and tendons will be exerted beyond their tone if the heels of the shoes are not gradually thinned as the horn grows, or as the toe of the crust can be removed.
'45. Young horses, with perfect feet, should not have thin-heeled shoes at first, unless the crust at the toe can be removed in the same degree as the iron at the toe exceeds the heels.
'46. Where half an inch of horn can be taken from the toe of the crust, a shoe thin at the heel may be at once applied without any injury to the muscles and tendons.
'47. Where the heels exceed two inches in depth, and the frogs are equally prominent, and the ground dry, a short shoe, thin at the heels, may be applied.