Aëtius, copying from Archigenes, thus marks the difference between lepra and its cognate diseases. Lepra differs from leuce and alphos, inasmuch as lepra is distinguished by roughness and a sense of itching, and yet the skin only is affected, and when it is removed, the flesh below is discovered to be sound; but in leuce, the flesh below assumes an unnatural degree of whiteness, while the surface of the part is very smooth, and when rubbed it soon becomes red, especially in those who are readily cured; and alphos is altogether superficial, having the appearance of a scale fastened to the skin. Lepra differs from psora, inasmuch as in psora the substances which appear on the skin are of a furfuraceous nature, while in lepra they resemble the scales of a large fish. He omits the constitutional treatment so judiciously stated by our author, but his local applications are little different. They contain hellebore, sulphur, misy, verdigris, liquid pitch, cantharides, natron, copperas, myrrh, galls, vinegar, &c., mixed in various proportions. Actuarius states that lepra is next to elephantia in malignity, and that it is distinguished from psora by spreading deeper and having scales of a circular shape like those of fishes; whereas, psora is more superficial, and its scales are furfuraceous and of no determinate shape. Both are attended with asperity of the skin, and itching. Leuce holds the same place to alphos that lepra does to psora, that is to say, leuce is more deep-seated, and affects the colour of the hair, while alphos is more superficial, and the hair is in general unchanged. For all these affections he recommends an application containing copperas, black hellebore, arsenic, and cantharides, mixed with oil, cedar resin, or rose oil. Psellus states correctly that the scales in leprosy assume a circular shape. Nonnus marks the distinction between these diseases very accurately. Lepra arises from a corroding humour, and hence scales fall from the surface of the skin, and it is attended with pruritus. But lepra is more deep-seated, and affects the skin circularly; whereas psora is more superficial and variously figured. Leuce and alphos albus and niger, he says, are allied; but leuce is deeper seated, so as to change the colour of the hairs, whereas the alphi are more superficial affections. Pollux, like most of the others, states that in leuce, when the skin is pricked, it does not bleed, and that the disease is difficult to cure. Alphos and melas, he says, are easily cured. Although Myrepsus has not described these diseases, he gives prescriptions for various compositions to remove them. The most active ingredients in them are hellebore, natron, sulphur, quicksilver, sal ammoniac, quicklime, bay-berries, &c. Alexander Aphrodisiensis mentions psora among the contagious diseases, but says that lepra and leuce are not contagious.