would bind, stimulating the cell to produce more of the same type, which would then be liberated into the blood stream as antibodies. According to Ehrlich, an antibody could be considered an irregularly shaped, microscopic, three-dimensional label that would bind to a specific antigen but not to the other cells of the organism. It was these antibodies that Ehrlich first described as "magic bullets", agents that specifically target toxins or pathogens without harming the body. Ehrlich suggested that interaction between an infectious agent and a cell-bound receptor would induce the cell to produce and release more receptors with the same specificity. According to Ehrlich’s theory, the specificity of the receptor was determined before its exposure to antigen, and the antigen selected the appropriate receptor. Ultimately all aspects of Ehrlich's theory would be proven correct with the minor exception that the "receptor" exists as both a soluble antibody molecule and as a cell-bound receptor; it is the soluble form that is secreted rather than the bound form released. See also Dr. Ehrlich's Magic Bullet, a 1940 film Diphtheria Syphilis References Further reading Immunology theories Paul Ehrlich