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In 1914, while teaching histopathology of the skin to medical students at the University of Michigan, I found it necessary in developing a dynamic comprehension of the field to lay stress on the fundamental pathologic unity which underlies the seeming diversity in the clinical pictures of the inflammatory dermatoses. In order to accomplish this purpose I analyzed the clinical picture of inflammation of the skin into nine component elements or cutaneous reaction signs, erythema, edema, vesiculation, oozing, crusting, scaling, lichenification, fissuring, and hyperpigmentation. Each feature of the clinically visible picture had its counterpart in some feature of the histopathologic picture. Subsequently at the University of Illinois I used a similar device to impress on students the distinction between acute and chronic dermatitis, on which therapeutic decisions so often depend.
In 1918 and 1919, in my lectures to the Fellows in the Mayo Foundation, I expanded the original scheme into the