The philosopher Marcus Antoninus alludes to the plague as being contagious. (ix, 2.) Chrysostom does the same. (In Joan. Orat. lvii.) The language of Seneca is very precise: “Itaque ut in pestilentiâ cavendum est ne corruptis jam corporibus et morbo flagrantibus assideamus, quia pericula trahemus, afflatuque ipso laborabimus.” (De Tranquil. vii.) To these we may join Isidorus Hispalensis, a much later writer: “Pestilentia est contagium quod quum unum apprehenderit celeriter ad plures transit.” And, in another place: “Pestilentia est morbus latè vagans et contagio suo quæ contigerit interimens.” Alexander Aphrodisiensis intimates that pestilential fevers are contagious, but common fevers not so. (Probl. ii, 42.) Aretæus appears to be the first medical author who alludes to contagion in unequivocal terms. He says of elephantiasis, that it is as infectious as the plague, being communicated by respiration. Cælius Aurelianus, who was probably nearly contemporary with him, mentions as contagious diseases the plague, incubus, hydrophobia, and elephantiasis. Galen expresses his sentiments on the contagious nature of certain diseases in the following terms: “That a pestilential state of the atmosphere produces fever, is unknown to no one possessed of good understanding; and, also, that it is dangerous to associate with persons having the plague, for there is a risk of catching it, like the itch and ophthalmy. It is dangerous also to live with those labouring under consumption, and, in a word, with all those having a putrid respiration of such a nature as to render the houses in which they lie fetid.” (De Diff. Febr. i, 3.) Aëtius (xiii, 120) and our author (iv, i) state their decided opinion of the infectious nature of the plague and elephantiasis. Oribasius, Alexander, Synesius, Palladius, Actuarius, and all the Latin medical authors, with the exception of Cælius Aurelianus, have omitted to make any allusion to the contagious nature of diseases. Of the Arabians, Rhases mentions, as diseases “which are transmitted from one person to another,” lepra (elephantiasis?), itch, consumption, and pestilential fever. These, he says, prove infectious, when one is shut up in a narrow house along with those labouring under them, or when one sits in the wind blowing from them. He states afterwards that ophthalmy and malignant pustules are sometimes contagious. (Ad Mansor. iv, 24; see also Contin. xxxiii, 5.) By malignant pustules he means the smallpox. Avicenna and Haly Abbas give the same list of contagious diseases. Avicenna says that smallpox and measles are of all diseases the most contagious. Of the other Arabians, Avenzoar alone, while treating of elephantiasis, alludes to the doctrine of contagion.