On Exercise and Motor Skill
Since ancient times, one of the specific features of human beings (and some closely related animals) has attracted the attention of intelligent people. Machines and tools deteriorate with use; they wear out, loosen up, and generally become worse. The best machines are those that do not require repair for long periods of time. The situation with the "human machine" is the opposite. The longer a human participates in a certain activity, the better he or she performs it. A living organism not only does not deteriorate during work but, quite the opposite, becomes stronger, quicker, more enduring, more adroit and dexterous, particularly with respect to the type of activity that has been performed. This feature of living organisms has been termed exercisability.
Frequently, it is harder to explain a phenomenon than to notice it and to use it in practice. This is true for exercisability, which happens to be a widespread phenomenon. After discovering it in animals, humans started to tame them, that is, to train and exercise them in helpful skills. However, the nature and essence of this basic difference between living beings and machines was difficult to discover.
Since long ago, physicians held tenaciously to a superstition, one they have just now begun to give up--the idea that live nature differs from "dead" nature by the presence of a so-called "vital force." Many phenomena were in need of explanation, an explanation that required the introduction of the notion of a "vital force." Everywhere one could see how living organisms energetically strug-