generality of their scientific findings. This reduction, however, should always be consistent with the necessity to replicate and validate important scientific findings.

The book is developed around the sources and recognition of pain and distress and the pharmacologic and nonpharmacologic methods of avoiding and controlling them. It was not planned as a source of information on experimental design. Nor was it designed as a training document, although it is hoped that it will be useful for this purpose. (A recent report of the Institute of Laboratory Animal Resources might be of more direct assistance with the development of training and education programs [NRC, 1990].)

Chapters 24 focus on what is known about pain, stress, and distress in humans and animals. They constitute an introduction to Chapters 57, which provide specific recommendations for the care and use of laboratory animals.

GENERAL CONSIDERATIONS OF THE BIOLOGIC IMPORTANCE OF PAIN, STRESS, AND DISTRESS

The ability to avoid, escape from, or control pain and other inducers of stress and distress is critical to the survival and well-being of many animals (Phillips and Sechzer, 1989). Mechanisms that contribute to those abilities involve biochemical, physiologic, or psychologic changes and can be expressed behaviorally as homeostatic processes of adjusting to altered environmental conditions. Such behavioral processes can be short-term and adaptive or, as in cases of chronic pain and other potential sources of distress, can continue to the point where they become maladaptive. Maladaptive behaviors serve as important signs of distress in laboratory animals and indicate that intervention or scientific justification is required.

It is sometimes difficult to determine whether an animal is undergoing a normal process of adapting to a state of stress, for which intervention might not be indicated, or is in distress. Animal species differ in how they manifest distress, whether from pain or from other sources, and this complicates its recognition. But many signs of distress are shared by various animal species, and the tendency to highlight differences, rather than similarities, makes the task of recognizing it more complex than necessary. A comment on acute stress is in order. Under some circumstances, an animal can experience intense stress of short duration that (because it is brief) does not usually result in maladaptive behavior, although it might affect the animal's well-being adversely. Acute stress can also reduce the quality of research results. When stress is discussed in this text, the reader should consider whether the discussion applies to acute, as well as chronic, stress.

There is a lack of agreement on the meaning of such terms as comfort, well-being, discomfort, stress, fear, anxiety, pain, and distress. The terms and classification of syndromes presented here can be used provisionally and refined as additional information and understanding become available. The definitions that follow are presented as aids to the recognition of pain, environmental stressors, and the responses they produce. They should help to form the basis for the selection of



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