2. what event(s) led to the birth of social medicine (efforts to improve public health)?

Social medicine is a field of medicine that studies the impact of the collective 
behavior of organized society on individuals and concentrate on the social, cultural, and economic impact of medical phenomena.
The rapid industrialization and urbanization at the turn of the 19th century led to the birth of social medicine. Many social problems erased in Europe, including increased low-wage workers, poor working conditions, lack of housing and sanitation facility. Diseases and deteriorating health conditions among industrial workers and in the low-income population were also serious. All these events led to the idea to define and analyze the relationships among medical issues, social factors and public affairs. These were systematically integrated into the framework of social medicine. 

Stimulants speed up the central nervous system.