162 DEVELOPMENT AND HEREDITY. 



pronounced result. At first glance, one might say 

 that such an experiment was merely interference 

 with the natural growth, and no true test of the 

 forces causing the shape of organs. But a moment's 

 reflection shows that if we can prove that a certain 

 condition of stress produces one arrangement of the 

 component particles, then every other arrangement 

 of particles must be due to some other condition of 

 stress, and a normal limb must have its condition of 

 stress as well as an abnormal one. 



The effect of shock or sudden jarring upon bones 

 may be compared to the effect of exercise upon 

 muscle — i.e. it causes the repair to exceed the 

 damage or waste. Shock differs from pressure in 

 that pressure does not relax often enough to 

 admit- of the repair of its ravages, whereas shock 

 is only momentary, and not only admits, but seems 

 to stimulate, repair. Pressure is like the over 

 exercise of muscle, causing degeneration ; shock is 

 like exercise, causing growth. If a bone be struck 

 on one end, or if a row of articulated bones be 

 struck, the shock is passed from one end of the 

 bone, or the row of bones, to the other. Accord- 

 ing to the discoveries in the science of physics, 

 the continued repetition of such shocks tends 

 to cause a new arrangement in the particles of 

 the object struck. A bar of metal takes on a new 



