DISEASES OF THE SKIN. 



No notice has been taken, in the following chapters, of the altera- 

 tions which the skin undergoes in the acute and chronic infectious 

 diseases. Lake other symptoms of measles, scarlatina, small-pox, 

 typhus, and syphilis, these cutaneous affections are to receive the 

 attention due them, when we come to discuss the subject of the infec- 

 tious diseases themselves, as they only form a single link in the chain 

 of nutritive disturbances to which these maladies give rise. 



We classify diseases of the skin as we do diseases of other organs, 

 according to the anatomical nature of the lesion which the disease 

 produces. We shall, therefore, have to speak of hypertrophy, atrophy, 

 hyperaemia, anaemia, haemorrhages, inflammations, neoplastic growths 

 and parasites of the skin. Since, however, it is in our power to observe 

 the variety in extent, in intensity of the morbid process, more accu- 

 rately upon the skin than upon other organs, and as we are able directly 

 to watch certain anomalies of secretions which are not accompanied by 

 palpable change of structure, diseases of the skin admit of a much more 

 minute classification than is possible in diseases of other organs. We 

 must so far conform to the practice of applying names to the cuta- 

 neous affections other than those belonging to the analogous lesions 

 upon other parts of the body, as to associate their proper pathological 

 and anatomical title with their customary name. Of the unpractical 

 and useless classification of the various forms of skin-disease into innu- 

 merable subdivisions, we shall merely make cursory mention. 



I. HYPERTROPHY OF THE SKIN. 



AN hypertrophy, involving all the component parts of the skin, 

 the connective tissue, the vessels, nerves, epidermis, hair, and glands, 

 only occurs in small isolated spots as a congenital anomaly. Most of 

 the prominent " mother's marks " belong to this class, as well as the 



