This is because their systems have become loaded with a superfluity of waste matter. And the latter not only makes them headachy and tired, but if the accumulation is allowed to go on unchecked, it deranges the vital organs, the kidneys particularly, and before long may actually set up organic disease. After that the strain on the whole bodily functions becomes greater and greater, until the breaking-point is reached. For as people grow older their organs have less power of throwing off waste material, and become less able to support one another when any weakness appears. These breakdowns are the most liable to occur in the case of athletes who have been accustomed to severe and active exercise all their lives. In them the system seems to have learned to depend, even more than in the case of other people, upon hard exercise to keep it in good condition. And when men of this type drop it too suddenly, the results are disastrous. Yet that is what so many of them tend to do. They are unable any longer to indulge in the violent games and training to which they have been accustomed, and they will not “lower themselves,” as I have heard it expressed, to take part in milder forms of recreation. Sometimes they even become too lazy to walk. Of course, no man can be expected to keep up his running, or take part in boat races, or practise putting the weight after he has passed a certain age. Nor would it be good for him to do so. Once he has passed thirty he must begin to take things a bit more slowly, and avoid taking part in athletic contests. For racing in any form involves a mental as well as a physical strain, and few men beyond that age can stand the stress of the two combined. Yet if he cannot race he can still row or run or whatever else it may be. Later on he may have to give these up also, and take to quieter forms of exercise. The secret lies in the gradual dropping off. And no man need complain, for there are plenty of outdoor games suited to every age and every constitution. [Sidenote: Value of exercise.] The great point is that everyone, men and women alike, must have exercise of some kind or other. For most of the vital of processes of the body depend upon it. It is the chief agent in burning up the waste matter in the system, reducing it to such a form as is most easily excreted by the different organs. It also keeps this waste on the move, and so brings it more freely into contact with those organs. Furthermore, it stimulates the action of the heart and lungs, and so invigorates the circulation, and supplies the respiratory tract with a more liberal allowance of oxygen. Then, freed from the incubus of the presence of this poisonous matter, the digestion improves, and the nervous system regains its wonted vigour once more. [Sidenote: Regularity.]