Since loss of blood volume is the initiating factor common to most types of traumatic shock, the therapeutic problem has been studied experimentally primarily from this point of view. Confusing or complicating factors, such as local trauma and the sepsis of trauma and anesthetics including barbiturates, have been eliminated by limiting the experimental method to simple hemorrhage in the unanesthetized animal, with or without morphine. Shock, so induced and maintained, exhibits all the classical phenomena expected and is responsive within certain variable limits of time and levels of blood pressure, to the restoration of all the shed blood. If the shock state is treated effectively first by a replacement of the blood volume deficiency, the shock is said to be "reversible" and as such does not represent a problem of challenging import.