by Larissa Anastácio da Costa Carvalho
In the antiquity, many cities protected their territories by surrounding fortifications, with giant gates and arches working as unique gateways. The Roman god Janus, known as the protector of entrances or new-beginnings, is represented by a head with two faces in opposite directions. The two faces of Janus symbolize the duality of nature. Well, nature itself is marked by dichotomy. What in nature cannot be good and bad at the same time? That is the origin of the term Janus effect.
A remarkable example of the Janus effect is the mustard gas (1,1-thiobis-2-chloroethane). Used as a chemical weapon during World War I, it causes serious inflammation of the