Avenzoar has given us an elaborate treatise on epidemical complaints. (iii.) The first cause of them which he mentions is a humid and warm state of the atmosphere, such as that to which Hippocrates ascribed the pestilence which afflicted Thasus in his time. (Epid. iii.) The other causes enumerated by him are the effluvia from dead bodies, stagnant air, the miasmata from stagnant and corrupted waters, and unwholesome food. (iii, 3, 1.) On the origin of epidemical diseases, especially the pestilence, see, in particular, Haly Abbas (Theor. v, 11.) The principal causes of the change of the atmosphere to a pestilential state, according to Haly, are the nature of the country and the season of the year. The former cause operates owing to the putrid effluvia arising from corrupted fruit, pot-herbs, &c., or the miasmata from marshes, cloacæ, or dead bodies, whether of men or cattle. It was from such causes, he remarks, that the plague of Athens derived its origin. The nature of the season, as it produces diseases in the vegetable, so does it also in the animal creation. As epidemical complaints, he mentions ephemerals, cynanche, smallpox, acute fevers, and other fatal diseases. Avicenna’s account of the origin of pestilential and epidemic diseases is taken almost entirely from Galen; he therefore enumerates as causes of them, a humid and warm state of the atmosphere, the stagnant air of caverns, the miasmata of lakes and marshes, and the effluvia from dead bodies. (iv, i, 4.) Alsaharavius enumerates exactly the same causes. (32.) Rhases’ account is mostly taken from Hippocrates and Galen. (Contin. xxx.) The historian Ammianus Marcellinus gives an ingenious disquisition on the origin of these diseases; but the distinction which he endeavours to establish in the following passage is not acknowledged by the medical authors in general: “Prima species luis _Pandemus_ appellatur, quæ efficit in aridioribus locis agentes caloribus crebris interpellari; secunda, _Epidemus_ quæ tempore ingruens acies hebetat luminum, et concitat periculosos humores; tertia, _Lœmodes_, quæ itidem temporaria est, sed volucri velocitate letabilis.” (xix, 4.) The causes of these complaints, as enumerated by him, are excessive heat, cold, drought, or moisture, effluvia from putrid bodies, and exhalations from the earth. According to Diodorus Siculus, the causes which gave rise to the pestilential epidemic which attacked the Carthaginian army in Sicily were the marshy nature of the country in which they were encamped, the bodies of the dead lying unburied, and the excessive heat of the season. (xiv.) He ascribes the plague of Athens to similar causes. (xii. 58.) SECT. XXXVI.—ON THE PLAGUE, FROM THE WORKS OF RUFFUS.