'Starting with the integument we see many organs are contractile sacs or multiples thereof which tubes or bags constitute the major part of the entire body' (1). The lungs are a collection of these universal contractile chambers connected in chains and bunches. Such containers typically have muscular walls which stretch and contract to fill and empty also valves or sphincters to regulate the flow between neighbouring chambers. The heart, stomach and uterus are familiar examples. In some systems (e.g. the digestive, renal and respiratory tracts) traffic is also between the milieu exterior and the milieu interior through the organ's wall which is part of the integument. These movements from organ to organ or milieu to milieu involve pressure variations generated by the concerted actions of the mural and valvular muscles. A muscle usually has a doppel-gänger so they are arranged in reciprocating pairs, supinators with pronators, flexors with extensors, chamber walls with sphincters etc.