Speed, and still more duration in running, are in proportion to the developement of the lungs, and consequently the volume of oxygen and blood which they can combine in their parenchyma at each respiratory movement. Thus, of two men, one having the abdominal members developed, and the other possessing good lungs, the former will run with the greatest speed for a short distance, but if the distance be considerable, he will soon be gained upon by the latter. A runner, after performing a certain space, is seized with a difficulty of breathing, long before the repetition of the contractions has produced fatigue in the abdominal members. To excel, therefore, in running, requires, like walking and dancing, a peculiar exercise. As the muscular contractions depend, for their principle of excitement, on the respiration, the chest should be firmly fixed, so as both to facilitate this, and to serve as a point of support for the efforts of the lower members. The best runners are those who have the _best wind_, and keep the breast dilated for the longest time. During the whole time of running, long inspirations and slow expirations are of the greatest importance; and young persons cannot be too early accustomed to them. To facilitate respiration towards the end of the race, the upper part of the body may be leant a little forward. Running should cease as soon as the breath becomes very short, and a strong perspiration takes place. MODERATE RUNNING. This is performed gently and in equal time, and may be extended to a considerable space. In practising this pace, it is necessary to fix the distance to be run; and this should always be proportioned to the age and strength of the runners. This exercise, more than all others, requires to be proceeded with in a progressive manner. If, at the first trial, you run too fast or too long a time, it may produce spitting of blood and headache, or aneurisms of the heart and principal vessels, especially if the weather be dry and cold. A moderately cool day may accordingly be chosen, a distance of three hundred feet measured, and the runners placed in a line at one end. They may then start, trot at the rate of about seven feet in a second to the opposite end, turn, and continue until they reach the spot whence they started. Frequent repetition of this is sufficient at first. Afterwards, they may run over this space, two, three, or four times without stopping; and the exercise may then be limited to this. It may, on subsequent days, be extended to five, six, and seven times the distance. Fatigue is then generally quite removed; and the run may either be continued farther, or the runners, if neither heated nor winded, may accelerate their pace. They may next attempt a mile in ten minutes; and repeat this, till, being gradually less and less heated, they can either extend the distance, or diminish the time, in any measured proportion. At this pace, six miles may afterwards be run in an hour. RAPID RUNNING.