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nature is expressed by the many names applied to the condition, of which the most common are the following:

Hysterical spine.

Neurasthenic spine.

Weak back.

Uterine backache.

Irritable spine.

Chronic lumbago.

Railroad spine.

Relaxation of the sacroiliac joints.

Among the laity the condition is often attributed to kidney disease.

Without denying the existence of cases in which this symptom is the result of diverse causes, such as actual uterine, spinal or sacro-iliac disease, we are inclined from the observations and experiments to be described to regard the term "statie backache" as more truly descrip­tive of the majority of these cases. By which term we mean pain due to back strain incurred by an undue effort to maintain body balance under the conditions of the individual physiology.

If the patient is a woman and any abnormality of her uterine system can be found, it is usually considered adequate reason for immediate treatment by the gyne­cologist. If some innocuous uterine peculiarity is oper­ated on in order to cure a backache which is dependent on an overstrain of the back muscles, the results are not likely to be gratifying to the patient or to add much to the reputation of the surgeon who performs the opera­tion. So, too, the orthopedic surgeon who devotes months of effort with apparatus and gymnastics to the relief of back strain caused by the faulty posture origin­ated by inflamed pelvic organs is likely also to fail.

Outside of the gynecologic treatment, patients of either sex are treated by jackets, corsets, plaster strap­ping, splints, pads, springs, belts, massage, vibration, gymnastics, heat, electricity, etc. The application of each one of these measures is empirical and the method of action of each is in general as little understood as the etiology of the condition for which it is used. If, instead of this blind work, a serious attempt is made to investigate the causes of the condition and to study its mechanics, it is possible that much confusion and many failures will be saved.

The following experimental study, which has occupied us for the past three and one-half years, was under­taken because of the frequency with which one of us in gynecologic and the other in orthopedic practice met such cases of chronic backache, especially in women, and the study was made a joint one been use we concluded that a consideration of the subject from our two different points of view would be more likely to be of use than two pieces of work done by each of us separately. No sooner had we started on our joint investigation, however, than we realized that neither of us had any exact comprehension of the causes or mechanism of the condition, matters which were evic1ently essential to any clear comprehension or study of the subject. We there­fore turned to a study of the literature of the mechanics of the erect posture and found at that time little but vague statements, founded mostly on accepted authority, reliable than on observation of the living individual by reliable scientific methods. We were, therefore, obliged to begin our work by formulating for ourselves methods

for the study of the mechanics of the maintenance of the upright position, and at the outset It became evident that any such study must start with a determination of the center of gravity of the body, and its relation to the supporting structures, because all lines of strain and all muscular balance depend obviously on such relations, and we desire here to express our indebtedness to Prof. Ira N. Hollis, of Harvard University, for advice generously given us on the mechanical side of our problem.

Our first two years and a half were, therefore, spent in a purely physiologic research, at the end of Which time we had perfected an apparatus for determining the center of gravity in the erect living individual.^[1] Up to the time of this, our contribution to physiology, there had existed so far as could be learned from a study of literature, no reliable method of estimating the position of the center of gravity of the body in the upright position. Various loose statements as to its location are given in literature, and there are a few carefully formulated attempt, to determine it by a study of the masses of the body post-mortem and their relntion to each other, but scarcely any two writers agree as to what the erect normal posture should be.^[2]

The method in previous use had been as follows: A cadaver was dismembered, the center of garvity for each arm and leg, the head and the trunk were separately obtained and, by a formula, the relation of these masses to each other in an ideal erect posture was calculated, and the center of gravity of the whole body in this pos­ture was then located therefrom. From our observations we believe that the position of the center of gravity obtained in this way is misleading and untrustworthy for translation to the living, because the results obtained have failed so markedly to agree with the actual position of the center of gravity in the actual erect posture as obtained by us.

A study of the well-known method of Borelli for deter­mining the center of gravity in the horizontal position suggested to us our method of determining the antero-