This paper defined disease as anything
impairing the normal state or functioning of the body as a whole or of any of its
parts, explaining how certain diseases are short lived, but severe, others chronic. The author classifies diseases by their cause and how
infectious they may be. From the paper: "Disease can be defined as anything
impairing the normal state or functioning of the body as a whole or of any of its parts. Some diseases are short lived, but they are accompanied by severe symptoms. Others are chronic, or diseases that last a long time. Diseases are classified by their cause; this could be a virus, bacteria, rickettsias, or protozoa. Fungi and parasitic worms can also cause diseases. Human, certain animals and insects, and infected objects can transmit only infectious diseases. Chemical and physical agents such as drugs, poisons, and radiation can also cause disease."