The brain, nerves, heart and muscles must be given some warning of the work they are expected, collectively, to perform. Ignorance of this fact has broken down many a young man who aspired to honors on the cinder-path. The necessity of getting all the parts of the body slowly in working order is well understood by trainers and jockeys on the racetrack, as is evidenced by the preliminary “warming up” they give their horses, although it is doubtful if the trainers could give any physiologic reason for the custom. I once asked an old darky trainer in the South why he always ran his horses just before a race, and he replied, “I’s got ter ile ’em up; jus’ ile ’em up.” Then he shouted to a little bow-legged coon on a big bay horse: “Youse, git a goin’ dar, Sam; git ’im iled up so I kaint heer ’im squeek――git de ile in ’is jints; go dar!” And Sam went on “iling ’im up.” Of the substances supplied to the muscles by the blood, oxygen is one the want of which is soonest felt. The muscle contains within itself a certain store of oxygen, but one which is by no means equal to the oxidizable substances. The muscle’s activity is dependent, to a great extent, on the _character_ and force of the blood-flow. It must be clear of waste products, and contain, as well, sufficient oxygen to keep up continually a renewal of energy. From what has been said, it will readily be seen that the result of a muscular task which an athlete wishes to perform, will depend primarily on his muscular bulk and on the conditions of these muscles and the rate at which he expends his capital; the test of his endurance will depend upon the condition of the other parts of his body and how rapidly they will carry off the quickly formed poisonous products and supply fresh ones. A large number of the lesser pugilists have died in the ring the last ten years. Scarcely one of these deaths was directly due to the force or severity of the blows struck, but because the fighters were “out of condition.” The writer, himself, once had an opponent in the amateur ring whose condition was so plainly unfit that he refrained from exerting forceful energy, but let the man poison himself, when a gentle cross-counter laid him out. He literally beat himself. What I have said about self-poisoning refers also to the nerves and brain. As the muscles work faster, so do the central nerve cells which send the stimulating impulses to these muscles. These latter cells become fatigued sooner than the muscles. This is a grand feature of physiologic economy; for, did not this condition exist, the muscles would work themselves to pieces――run wild, like an uncontrolled engine. The muscular differences noted in individuals are in reality the difference in the nerve cells, the actions of the muscles indicating the activity of the central nervous system. When the muscles are being exercised the nerve cells indirectly determine the muscular activity.