A perfectly satisfactory classification of skin diseases has not yet been promulgated. To exemplify some of the difficulties which must be surmounted, a few references to past endeavors in this line will prove instructive. Mercuralis in the sixteenth century introduced a regional classification by grouping skin diseases according to their regional situation, without special regard for the nature of the lesions themselves. This arrangements sufficed for more than a hundred and fifty years, when Turner cutaneous diseases into two general classes, of the head and of the body, each with several divisions and sub- divisions, intended to show the differences of the lesions as to shape and other qualities. To eruptions of uncertain location, he gave such names as syphilides, psorides scrofulides, ephilides, etc., some of which continue in use at the present day. In 1776 Plenck made the first classification based on the objective character of the primary and secondary lesions or the parts involved, as follows:
12. Cutaneous Insects,
13. Diseases of the Nails.
14. Diseases of the Hair. Willan, and subsequently Bateman, modified Plenck’s classification, reducing the different classes to nine: Papules, Scales, Exanthemata, Bullae, Pustules, Vesicles, Tubercules, Macules and Dermal Excrescences. Next in importance came the anatomical classification of Erasmus Wilson who grouped skin diseases according to the part in which they originated, as
1. Diseases of the Derma,
2. Diseases of the Sudoriparous Glands,
3. Diseases of the Sebaceous Glands,
4. Diseases of Hair and Hair follicles.
A simple physiological plan of grouping cutaneous diseases was formulated by Barensprung, who suggested (1) Disturbances of Innervation, (2) Disturbances of Secretion, (3) Disturbances of Nutrition.
The best known and most popular system is that elaborated by Rokitansky and Hebra in 1845 and with modifications, it is still employed as the best framework for practical use. They classified dermatoses by their pathological anatomy, except one group, diseases caused by parasites, where the etiological factors were recognized. The classes of this system are
12. Diseases caused by parasites.
As illustrating real endeavor toward scientific classification should be mentioned the radical system of Auspitz (1881), as elaborated by Bronson in 1887, wherein the anatomical seat of the disease is taken as the basis and the pedigree of diseases is shown by subdivisions into orders, tribes, families, genera, and species. While undoubtedly scientific, this scheme is too complex and detailed to serve the student as a basis for satisfactory work.
Bazin and other French writers have sought to classify skin diseases according to their real or supposed causes. Bazin suggested three divisions: (1) Affections due to external causes, (2) Affections of internal origin, including those consecutive to some constitutional disorder, (3) Cutaneous deformities, congenital or acquired. In the effort to perfect this system, a relation was assumed to exist between certain constitutional diseases and cutaneous eruptions, which had little foundation in fact. An increasing knowledge of etiology will, in all probability, eventually permit a practical classification of cutaneous diseases according to their principal etiological relations. Unna, Piffard and others have proposed classifications in this line but these suggestions have not been generally accepted. Actuated by a desire to avoid the inconsistencies of these classifications, some of the American and French authors have adopted the alphabetic arrangement. This may be an easy way out of the difficulty and is satisfactory in epitomal treatises and quiz compends. However, I believe that a classification, no matter how imperfect, based on pathological and anatomical features, contains enough information to the student to warrant its adoption. Hence, in this book, I have employed the Hebra system as modified by Crocker and Duhring, plus changes warranted by recent investigations and my own experience.