This chapter concentrates on ideas of physical health and disease, which is not to minimize the importance of psychiatric disease, but rather to admit that concepts of mental health and illness, although sharing most of the definitional difficulties of physical health and disease, are even more difficult to handle. Granted that cultural, social, and individual considerations contribute to the expression of diseases in society, people may not overlook the importance of the biological aspects unique to diseases. A current example is the acquired immune deficiency syndrome (AIDS). The period of time between infection with the human immunodeficiency virus (HIV) and the body's development of a testable antibody response can be as long as a year. Hippocratism is cherished today because it is more congenial to modern medicine than the other competing systems of the time. After 1830s, neurologists began classifying diseases as organic and functional, the latter reserved for conditions in which current technology could not demonstrate structural alterations.