Summary
This quote suggests that large groups of people ("masses") tend to be susceptible to the spread of psychological or mental "epidemics." In other words, when people come together in large numbers, there is a heightened risk for collective behaviors, emotions, or beliefs to quickly and widely influence the individuals within the group. The quote implies that these psychic epidemics can shape and influence the thoughts, attitudes, and actions of the masses, highlighting the potential power and impact of collective psychology on society.