What Are These Tests Locating?
In the main the problems that affect general health lie in the spinal and cranial regions, as do most of the areas of dysfunction dealt with by those osteopaths whose work is confined to the aches and pains of the musculo-skeletal system. Spinal lesions display limitations of mobility, spasms of the related musculature with ligament involvement, swelling and congestion, sensitivity to pressure, and usually some degree of asymmetry. If such a state is prolonged, then chronic inflammation, fibrotic changes contractures and arthritic changes (calcium deposits), will show themselves. Whether acute or chronic, and regardless of which of the above mentioned changes have taken place, nerve impulses will be transmitted to the central nervous system from such a lesion. These will influence other segments of the spine and affect the organs or tissues supplied from the level of the lesion. There may also, of course, be local discomfort, pain and disability.
Spinal dysfunction may also result in reflex activity from an organ to the spinal segment that supplies it. As Paul Isaacson, D.O., says:
From a purely anatomic viewpoint, it would seem clear that a stress or strain applied to any one spinal articulation, regardless of cause, would involve several others to some degree. It would manifest itself by varying degrees of disturbance to the body mechanics, affecting posture, muscular tone, circulation, reactions to the nervous system and visceral function. At first these disturbances would be physiological, or functional, and reversible, but if allowed to persist might in time produce organic or irreversible changes in the tissues and viscera. Conversely, a primary lesion in a viscus (organ) may predispose the musculature and ligaments, innervated by the respective segments, to lesioning. 
Fundamental to the successful application of any osteopathic diagnostic methods, is a highly developed tactile sense coupled with a sound knowledge of human anatomy, physiology and pathology. The ability to diagnose changes in tissue texture, symmetry and the quality and range of joint movement, presupposes a knowledge of what is normal and healthy. The experienced osteopath is able to detect changes in texture, temperature, contour and relative moisture on the surface of the skin. By palpating he can assess deeper tissue changes such as increased tension and fluid content. He can readily tell the difference between the state and quality of superficial and deeper muscles. By feeling and looking he can assess imbalance in structure and asymmetry and can then detect gross and subtle changes in joint mobility. This is sometimes the earliest sign of joint dysfunction.
The development of the skills required for such work involves persistent effort and practice. The osteopath must be able to receive, through the hands, the messages that are present in the tissue. These must be correctly assessed and interpreted before therapy can be meaningful or successful. Correct diagnosis is essential to successful treatment.
Dr Viola Fryman has written as follows regarding what may be discovered via palpation. 
- A very light touch, even passing the hand a quarter inch above the skin, provides information on the surface temperature. An acute lesion area will be unusually warm, an area of long standing, chronic lesion may be unusually cold as compared to the skin in other areas.
- Light touch will also reveal the cutaneous humidity, the sudorific (perspiration) or sebaceous (oily secretion) activity of the skin.
- The tone, the elasticity, the turgor of the skin may be noted by light pressure.
- A slightly firmer approach brings the examiner into communication with the superficial muscles to determine their tone, their fullness, their metabolic state.
- Penetrating more deeply, similar study of the deeper muscle layers is possible.
- The state of the fascial sheaths (fibrous tissue enveloping the muscles).
- In the abdomen similar palpation will provide information about the state of the organs within.
- On deeper penetration, firm yet gentle, contact is reached with bone.