The contributions of Tarde to social thought have stimulated numerous investigators to enter the field of social psychology. While Tarde’s thinking has been severely criticised by the psychologists and modified by the sociologists, it has opened mines of valuable social ores. Not the least important consideration was the impetus which the Tardian thought gave to American writers, such as E. A. Ross.[XXII-34] Tarde’s name, however, will be long revered for the penetrating way in which he developed the concept of imitation. Although Walter Bagehot, an English publicist, in an epoch-stirring book, _Physics and Politics_, published an important chapter on “Imitation” as early as 1872, it was Tarde’s _Lois de l’imitation_ in 1890 which at once became the authority on the subject. In the United States, Michael M. Davis, Jr., has written an excellent summary of Tarde’s socio-psychologic thought.[XXII-35] As a critical digest of Tardian thought, Dr. Davis’ _Psychological Interpretations of Society_ is unsurpassed. In 1892, Profesor H. Schmidkunz published an elaborate work on the _Psychologie der Suggestion_. This book is an important pioneer work. In the English language, the writings of Boris Sidis on the psychology of suggestion are well-known. Professor E. A. Ross has given an intensive treatment of the theme in his _Social Psychology_. In these various discussions, however, the fact is not made clear that suggestion and imitation are correlative phases of the same phenomenon. The point, also, is not developed that suggestion-imitation phenomena are natural products of social situations in which like stimuli normally produce like responses. In 1895, the first book by Gustave Le Bon on crowd psychology was published. Le Bon has also written on the psychology of revolutions, of war, and of peoples. He gave a limited definition to the term, crowds, and then applied the term to nearly all types of group life. He conceived of crowds as “feeling phenomena.” They are more or less pathological. Since the proletariat are subject to crowd psychology, they are untrustworthy and to be rewarded perpetually with suspicion. A sounder, more synthetic, and historical position concerning the psychology of groups and of society is taken by G. L. Duprat in _La Psychologie sociale_.