Page:Popular Science Monthly Volume 38.djvu/488

472 matters. The form of the curvings of the vertebral column depends on the action of the weight and of the antagonistic muscles that bend and extend it. There is an evident relation between the curves of the vertebral column and the form of the thorax; with large curvatures correspond depression of the ribs, and enfeebling of the thorax and its consequences—obstruction of the circulation and of pulmonary ventilation.

The respiratory capacity of a person does not depend on the absolute volume of the throat, but on the extent to which its volume increases between expiration and inspiration. The lung is the slave of the thoracic wall, and follows it in all its movements. It is constantly kept in contact with that wall, through the action of the atmospheric pressure, which is transmitted to the interior of the bronchise, whenever the glottis is opened. Except under stress of effort, we can not imagine the lung pushing upon the thoracic wall to dilate it; the contained has to submit to the variations of the containing. Hence, we have no reason to wonder that gymnasts are soon able, by training, to increase their respiratory capacity by giving, through the motions of the upper limbs, a great mobility to the articulations of the thorax, and thus permitting it to dilate more freely under the action of the elevator muscles of the ribs, to the effect of which is added that of the diaphragm. By strengthening the shoulder and fixing the omoplate with strong muscles, we furnish points of support, in raising the ribs and the flattened thorax. The action of the muscles of the abdominal walls counterpoises that of the extensors of the trunk, and the spine is raised by diminishing its curvatures under the effect of these two kinds of curves acting upon it as upon a bow with two curves. Thus, by perfecting the muscular powers and bringing them into equilibrium, the trunk assumes a good attitude, the chest expands, and the man bears the external indications of vigor and health. % All these observations are facts demonstrated and known by practitioners, who have obtained them through good gymnastics. They show that there is a direction to be given to exercises having a good result in view, and that the purpose of physical education will be more quickly attained as the methods are more precise. Stirring around in an indeterminate way is certainly not the shortest and most direct means of obtaining the essential modifications sought for.

We have attached so much importance to that part of the hygiene of exercise that bears upon the form, that we have had constructed at the physiological station, with the assistance of M. Otto Lund, an arsenal of instruments of measurement of a new kind. Some of these instruments give the height, weight, and outline in true size of the fore and back curvatures of the spine; others furnish complete sections of the trunk on a horizontal and