humoral theory
noun
1The theory that the balance and condition of the four humours, or (in later use) the body fluids generally, are responsible for states of health and disease; any theory of this nature (now historical ).
2Any theory attributing a physiological role to specific chemical substances in the body fluids; (Immunology ) the theory that immunity, or a specific immunological phenomenon, is dependent upon the action of antibodies rather than cells.
Origin
Late 18th century.