In the 3rd century B.C., Hippocrates stated the concepts of health. He believed there were 4 humors: blood, yellow bile found in the gall bladder, black bile found in the spleen, and phlegm found in the pituitary gland.
Several centuries later Galen developed a comprehensive system to explain bodily function and disease processes (Figure 1). He added to Hippocrates ideas, by stating that there were three spirits: natural spirit of the liver, vital spirit of the heart, and animal spirit of the brain. Galen's dogma of medicine remained essentially unchanged for 1500 yrs.
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