move from one subject to another. Chapter 1, in this volume offers the bridge to Volume 23 and its final Chapter 7. This Volume 24 contains contributions pertaining to cell activities and the environment. Chapters 1-4 refer specifically to interactions between cells and the integration of cell activities. The focus is on a functional immune system, with antigenic challenge as a subtopic. In Chapters 5-7, the environment is considered from several points of view and the main subtopic here is the result of the consequences of connections and missed signals. The internal and external environments are treated, revealing what may happen when normal immune responses are interfered with. All this is integrated by the consideration of the three great regulatory systems, the ever-present network that somehow acts as the monitor or control for all incoming and outgoing signals.