Variations in Stature due to Mechanical Causes of Adaptation to Environment
Variations due to Mechanical Causes. Transitory and Permanent Variations. Deformations.—The individual stature is not a fixed quantity at all hours of the day; but it varies by several millimetres under the influence of mechanical causes connected with the habits of daily life. In the morning we are slightly taller than at night (by a fraction of a centimetre): in consequence of remaining on foot a good deal of the time during the day, our stature is gradually lowered. This is contrary to the popular belief that "while we stand up our stature grows."
As a matter of fact, in the erect position the soft tissues that form part of the total stature are under constant pressure; but being elastic, they resume their previous proportions after prolonged rest in a horizontal position.
Consequently at night, especially if we have taken a long walk, or danced, we are shorter than in the morning after a long sleep; the act of stretching the limbs in the morning completes the work of restoring the articular cartilages to their proper limits of elasticity. Nevertheless, according to the mechanical theory accepted by Manouvrier, persons who are habituated from childhood to stand on foot much of the time (labourers) interfere with the free growth of the long bones in the direction of length and at the same time augment the growth in thickness; hence the skeleton is rendered definitely shorter in its segments as well as in its bones (i.e., a shallower pelvis, shorter limbs, etc.). The result is a stocky type with robust muscles: the europlastic type, which is found among labourers. On the contrary, a person who spends much time reclining on sofas among cushions, and taking abundant nutriment, is likely to tend toward the opposite extreme; bones long and slender, the skeleton tall in all its segments, the muscular system delicate; this is the macroplastic or aristocratic type. According to Manouvrier, when a person has a long, slow convalescence after a protracted infectious malady such as typhoid, recumbent much of the time and subjected to a highly nutritive diet, it may happen, especially if he has reached the period of puberty at which a rapid osteogenesis naturally takes place in the cartilages of the long bones, that he will not only become notably taller, but will even acquire the macroplastic type.
The macroplastic type is artistically more beautiful, but the europlastic type is physiologically more useful.
It is not only the erect position that tends to reduce the stature, but the sitting posture as well. In fact, whether the pelvis is supported by the lower limbs or by a chair, the intervertebral disks are in either case compressed by the weight of the bust as a whole. If, for example, children are obliged, during the period of growth, to remain long at a time in a sitting posture, the limbs may freely lengthen, while the bust is impeded in its free growth, and the result may be an artificial tendency toward macroscelia. This is why children are more inclined than adults to throw themselves upon the ground, to lie down, to cut capers, in other words to restore the elasticity of their joints, and overcome the compression of bones and cartilages. Accordingly, such variations of stature recur habitually and are transitory, and since they are associated with the customary attitudes of daily life, they are physiological.
But if special causes should aggravate such physiological conditions, and should recur so often as not to permit the cartilages to return completely to their original condition, in such a case permanent variations of stature might result, and even morphological deviations of the skeleton. For example, a porter who habitually carries heavy weights on his head, may definitely lower his stature; and in the case of a young boy, the interference with the growth of the long bones through compression exerted from above downward, may produce an actual arrest of development of the limbs and spinal column, presenting all the symptoms of rickets. Witness certain consequences of "child-labour" chief among which must be mentioned the deformities of the carusi [victims of child-labour, who from an early age toil up the succession of ladders, bearing heavy burdens of sulphur from the mines below.[18]] in the Sicilian sulphur mines.[19] As a general rule, all cramped positions that are a necessary condition of labour, if they surpass the limits of resistance and elasticity of the human frame, and especially if they operate during periods of life when the skeleton is in process of formation, result in deformities, and when the skeleton is deformed, the internal organs and hence the general functional powers of the whole organism, suffer even greater alteration.
Fig. 25.—Vincenzo Militella of Lereata, a Sicilian caruso.
