774 THE POPULAR SCIENCE MONTHLY.
preserve a degree of immunity for exhausting exercises longer than the average are those whose circulation has remained regu- lar, and whose arteries have not yet begun to undergo sclerotic degeneration. They are really younger than their age. Every man, according to the happy expression of Cazalis, is " of the age of his arteries/' and not of that which he deduces from his birth. Taking a mean, we may say that after forty years a man ought to abstain from exercises that induce shortness of breath. Instead of exercises of speed, he should adopt those requiring bottom, for which he will preserve a remarkable capacity. Race-horses which have become incapable of enduring labor that involves speed may for many years afterward perform excellent service at more mod- erate paces ; they may even easily endure the paces of the hunt, when they have to carry their rider for the whole day, but in which the fundamental gait is not the gallop but the trot. So man preserves to the extreme limits of mature age the faculty of enduring a considerable labor for many hours, provided it is car- ried on with moderation. Many of the best mountain guides are approaching their sixties, and can easily tire young tourists. But everybody has remarked that the most experienced guides that is, the oldest ones go up very slowly, and that under that con- dition they can walk for an indefinite time. They do this by avoiding, through the moderation of their pace, the quickening of their pulse and the imposition of an excess of work on their heart.
In 1870, when the dangers of the invasion called all French citizens to take part, each one according to his ability, in the de- fense of the country, national guards of the reserve were organ- ized everywhere, in which all those who for any reason had not been incorporated in the active service were enrolled. In the exercises of these improvised battalions, men of very unequal ages could be seen elbowing one another in the ranks. Many of them, who had passed their fortieth year, but felt themselves still "game," came to take part in the manoeuvres, and were never behind in the long drill-marches. Generally, indeed, the elderly men displayed a greater power of resistance than the younger ones. But their superiority vanished as soon as the manoeuvres took the form of quick movements. The " gymnastic step " was the terror of these well-intending veterans ; after one or two min- utes of the run they could be seen leaving the ranks out of breath, while the younger ones, whom they had left behind on the long marches, kept on for a considerable time without feeling any obstruction to their breathing. Serious accidents were sometimes produced in these movements, when they were commanded by too zealous officers who forced the men to keep up their speed not- withstanding the difficulty in their breathing ; and national