I have said that the horse's breathing can not be free so long as a large belly interferes with the action of the lungs. To lighten a large carcass is to improve the wind. But I am persuaded that the lungs themselves may undergo a change particularly favorable to protracted exertion. Though I can not offer any proof of this, I think the alterations which take place in other parts of the body make it appear probable that the lungs also are altered. It is reasonable to suppose that the tubes which carry the blood, and those which carry the air, suffer some increase of calibre; and that the lungs taken altogether, become a little larger. Such an alteration seems necessary to account for the visible change which takes place in the breathing. As training proceeds, the horse becomes less and less distressed by exertion, and ultimately acquires the power of doing that which would have killed him at the beginning; and the cause of death would have been found in the lungs. I can offer no other proof in favor of this supposition. It will be observed in many parts of this work, that I am compelled to suggest in ■ quiry when it would have been more pleasant to state the result of inquiry already made.

But these matters have been so much neglected, that it does not seem to have occurred to anybody that investigation is needful. Our knowledge is incomplete, yet no one speaks as if there were anything to learn. [It is far more complete than our author thought. He had not learned it himself, and commits the error of thinking that no one else had.]

It is well enough known, however, that to improve the wind the horse must have a great deal of exertion. Purgi g, sweating, and other emaciating processes, remove all obstruction to the lungs; exertion, at such a pace as to quicken the breathing, does the rest. But all horses do not need the same quantity of work to improve their wind. In some it is naturally very good. They have large nostrils, a wide wind pipe, and a deep chest. By proper training their breathing becomes remarkably free and easy; hardly any pace or distance produces distress. They go as far and as fast as the legs can carry them. When over-worked it is generally the legs, not the lungs, that fail. There are as many other horses whose wind is bad, never very good by any management. They have small nostrils, and a small chest,.neither deep nor wide. In these the wind fails before the legs; work makes the others leg-weary; these it over-marks, producing congestion, or inflammation in the lungs. These horses are never fit for long races.

However good or bad the wind may be before training, it always improves more or less as training proceeds. It is improved at the same time, and by the same means, that power is giver to the muscular system. But exertion may be so regulated that the muscular system shall acquire all the energy of which it is capable, and yet the wind may be neglected and defective. Short distances give power and alacrity to the muscles, but long distances are necessary to improve the wind. The horse must go far enough and fast enough to quicken the breathing, but not at any time so far nor so fast as to distress him very much. When the chest is defective, or when there is a strong tendency to the formation and accumulation of fat, the horse may need a great deal of exertion to render his wind fit for his work; and, in either case, he must have good legs to stand the exertion. When the legs and the chest are both defective, the horse will turn out a very or dinary animal. He will last longer at slow than at fast work.