The pellagra of the North Italian peasantry (and of Roumania, Gascony and some other limited areas) is the nearest affinity to leprosy among the species of disease. Strip leprosy of all its superficial and sentimental characters, analyse its essential phenomena, reduce its pathology to the most correct outlines, and we shall find it a chronic constitutional malady not far removed in type from pellagra. In both diseases there are the early warnings in the excessive sensibility, excessive redness and changes of colour, at certain spots of skin on or about the face or on the hands and feet. In both diseases, permanent loss of sensibility follows the previous exaggeration, blanching of the skin will remain for good at the spots where redness and discoloration were apt to come and go, and these affections of the end-regions of nerves will settle, in less definite way, upon the nervous system at large,--the cerebro-spinal nervous system, or the organic nervous system, or both together. What makes leprosy seem a disease in a different class from that, is the formation of nodules, or lumps, in the regions of affected skin in a certain proportion of the cases. If leprosy were all anaesthetic leprosy, its affinities to pellagra would be more quickly perceived; it is because about one-half of it has more or less of the tuberculated character that a diversion is created towards another kind of pathology. But the fact that some cases of leprosy develop nodules along the disordered nerves does not remove the disease as a whole from the class to which pellagra belongs. In both diseases we are dealing essentially with a profound disorder of the nerves and nerve-centres, commencing in local skin-affections which come and go and at length settle, proceeding to implicate the nervous functions generally, impairing the efficiency of the individual, and bringing him to a miserable end. The two diseases diverge each along its own path, leprosy becoming more a hopeless disorder of the nerves of tissue-nutrition, and so taking on a structural character mainly but not exclusively, and pellagra becoming more a hopeless disorder of the organic nervous system (digestion, circulation, etc.) with implication of the higher nervous functions, such as the senses, the intellect, and the emotions, and so taking on a functional character mainly but not exclusively. The correlation of structure and function is one that goes all through pathology as well as biology; and here we find it giving character to each of two chronic disorders of the nervous system, according as the structural side or the functional side comes uppermost.