Egg, larva, pupa and adult
Bacterial infections were much harder to treat a long time ago because we didn't have the same technology or information that we do now. because we have worked so long on treating different things we have learned what works and what doesnt. the new technology has helped us understand the infection which led to us being able to find medication to treat said infection.
It is pH. If you have a pH of 0-6 it is a acidic. If you have a pH of 7 it is neutral. If you have a pH of 8 or above it is a base.