It is a comforting fact that the human body confronted by Hippocratic physicians is the same as that treated by doctors of today, and that no differences are expected to appear tomorrow. However, although the structure and function of the body are enduring facts, medical science and physicians of different eras have behaved as if they were dealing with a body that itself is different. It is their conceptions of how the body works that in large part determine the behavior of physicians in its regard. While beliefs about structure and function are rooted in the reality of the body, there can be no doubt about the changes in these ideas through the ages. Such a change appears to be occurring during this century as a result of which the body is reacquiring the purpose it lost in the eighteenth century.