66 THE HUMAN BODY 



walk on the tips of their toes and fingers; and those animals, as 

 bears and apes, which like man place the tarsus also on the ground, 

 or in technical language are plantigrade, have a much less marked 

 arch there. The vaulted human tarsus, composed of a number of 

 small bones, each of which can glide a little over its neighbors, but 

 none of which can move much, is admirably calculated to break 

 any jar which might be transmitted to the spinal column by the 

 contact of the sole with the ground at each step. A well-arched 

 instep is therefore rightly considered a beauty; it makes progres- 

 sion easier, and by its springiness gives elasticity to the step. In 

 London flat-footed candidates for appointment as policemen are 

 rejected, as they cannot stand the fatigue of walking the daily 

 "beat." 



Hygiene of the Bony Skeleton. In early life the bones are less 

 rigid, from the fact that the earthy matters then present in them 

 bear a less proportion to the softer organic parts. Hence the bones 

 of an aged person are more brittle and easily broken than those of a 

 child. The bones of a young child are in fact tolerably flexible 

 and may be distorted by any continued strain; therefore children 

 should never be kept sitting for hours, in school or elsewhere, on a 

 bench which is so high that the feet are not supported. If this be 

 insisted upon (for no child will continue it voluntarily) the thigh- 

 bones will almost certainly be bent over the edge of the seat by the 

 weight of the legs and feet, and a permanent distortion may be 

 produced. For the same reason it is important that a child be 

 made to sit straight while writing, to avoid the risk of producing 

 a lateral curvature of the spinal column. The facility with which 

 the bones may be molded by prolonged pressure in early life is 

 well seen in the distortion of the feet of Chinese ladies, produced 

 by keeping them in tight shoes; and in the extraordinary forms 

 which some races of man produce in their skulls, by tying boards on 

 the heads of the children. 



Throughout the whole of life, moreover, the bones remain among 

 the most easily modified parts of the Body; although judging from 

 the fact that dead bones are the most permanent parts of fossil 

 animals we might be inclined to think otherwise. The living bone, 

 however, is constantly undergoing changes under the influence of 

 the protoplasmic cells imbedded in it, and in the living Body is 

 constantly being absorbed and reconstructed. The experience of 



