other of the general and local effects of exercise. It is in the earliest period of mature age that the most characteristic manifestations of defects of nutrition—obesity, gout, and diabetes, in which lack of exercise plays an important part—are produced; and the treatment of them demands imperiously a stirring up of the vital combustion. Placed between a conviction that exercise is necessary, and a fear of the dangers of exercise, the mature man ought, therefore, to proceed with the strictest method in the application of this powerful modifier of nutrition. It is impossible, however, to trace methodically a single rule for all men of the same age, for all do not offer the same degree of preservation. We might, perhaps, find a general formula for the age at which the muscles and bones have retained all their power of resistance, and at which the heart and vessels begin to lose some of their capacity to perform their functions. The mature man can safely brave all exercises that bring on muscular fatigue, but he must approach with great care those which provoke shortness of breath.
The formula is thus subjective in its application, in the sense that it looks rather to the feeling of the person than to the exercise itself; and from this point of view it is exactly applicable to all. One person is taken with shortness of breath at the beginning of a fencing bout; another one of the same age can fence without losing breath, while he tires his legs and arms. Most frequently the question of measure in the practice of exercise is more important than the choice of the kind. Some exercises are dangerous only on account of the temptation they offer to impetuous temperaments to pass beyond reasonable bounds. Thus fencing, which prematurely wears out too enthusiastic swordsmen, may remain a very hygienic exercise for the man of fifty years, provided he is enough master of himself to moderate his motions. There are exercises, however, which of themselves imply the necessity of a violent effort or a rapid succession of movements; among these are some of the exercises with gymnastic apparatus, wrestling, and running. These should be absolutely prohibited to the elderly man. This rule can not be invalidated by the rare examples of men who have been addicted to such exercises till an advanced age. Such men have continued, in respect to their structure, younger than their age; they have kept their elastic arteries as other persons keep their black hair. They are physiological exceptions, and general formulas do not regard exceptions.
The need which the elderly man feels of a stimulation of his organic combustion may be satisfied in other ways than by exercises of strength and agility. It is, in fact, the sum of work that regulates the quantity of heat expended by the human body, and
