B. Social Contact in Relation to Solidarity and to Mobility 1. The In-Group and the Out-Group. _W. G. Sumner_. 293 2. Sympathetic Contacts versus Categoric Contacts. _N. S. Shaler_ 294 3. Historical Continuity and Civilization. _Friedrich Ratzel_ 298 4. Mobility and the Movement of Peoples. _Ellen C. Semple_ 301 C. Primary and Secondary Contacts 1. Village Life in America (from _the Diary of a Young Girl_). _Caroline C. Richards_ 305 2. Secondary Contacts and City Life. _Robert E. Park_. 311 3. Publicity as a Form of Secondary Contact. _Robert E. Park_ 315 4. From Sentimental to Rational Attitudes. _Werner Sombart_ 317 5. The Sociological Significance of the "Stranger." _Georg Simmel_ 322 III. Investigations and Problems 1. Physical Contacts 327 2. Touch and the Primary Contacts of Intimacy 329 3. Primary Contacts of Acquaintanceship 330 4. Secondary Contacts 331 _Bibliography: Materials for the Study of Social Contacts_ 332 _Topics for Written Themes_ 336 _Questions for Discussion_ 336 CHAPTER VI. SOCIAL INTERACTION I. Introduction 1. The Concept of Interaction 339 2. Classification of the Materials 341 II. Materials A. Society as Interaction 1. The Mechanistic Interpretation of Society. _Ludwig Gumplowicz_ 346 2. Social Interaction as the Definition of the Group in Time and Space. _Georg Simmel_ 348 B. The Natural Forms of Communication 1. Sociology of the Senses: Visual Interaction. _Georg Simmel_ 356 2. The Expression of the Emotions. _Charles Darwin_ 361 3. Blushing. _Charles Darwin_ 365 4. Laughing. _L. Dugas_ 370 C. Language and the Communication of Ideas 1. Intercommunication in the Lower Animals. _C. Lloyd Morgan_ 375 2. The Concept as the Medium of Human Communication. _F. Max Müller_ 379 3. Writing as a Form of Communication. _Charles H. Judd_ 381 4. The Extension of Communication by Human Invention. _Carl Bücher_ 385