What is Life ?

The enigma of life is still one of the two or three most difficult problems that face both scientist and philosopher, and notwithstanding the progress of knowledge during the past twenty-three hundred years we do not seem to have advanced appreciably beyond the position of Aristotle in regard to the main issue. What are its characteristic manifestations? What are its chief forms? What is the inner nature of the source of vital activity? How has life arisen? Such are among the chief questions which present themselves with regard to this subject.