Complex sentence: The discovery of the world of microorganisms can be dated back to the seventeenth century, when German physician Robert Koch introduced the science of microorganisms to the medical field, identifying bacteria as the cause of infectious diseases and process of fermentation in diseases.
Split into simpler sentences: The discovery of the world of microorganisms can be dated back to the seventeenth century, when German physician Robert Koch introduced the science of microorganisms to the medical field. He identified bacteria as the cause of infectious diseases and process of fermentation in diseases.