THE INNER TISSUES OF ANIMALS. 343 



ftuch cases occur in ricketty children. I am indebted to ]\Jr. 

 Busk for pointing out these abnormal formations of dense 

 tissue, that are not apparently explicable as results ot 

 mechanical actions and re-actions. It was only on tracing 

 out the processes here at work, that there suggested itself the 

 specific interpretation of the normal process, as above set 

 forth. When, from constitutional defect, bones do 



not ossify with due rapidity, and are meanwhile subject to 

 the ordinary strains, they become distorted. Remembering 

 how a mass which has been made to yield in any direction 

 by a force it cannot withstand, is some little time before it 

 recovers completely its previous form, and usually, indeed, 

 undergoes what is called a " permanent set ;" it is inferable 

 that when a bone is repeatedly bent at the same time that 

 the liquid contained in its capillaries is poor in the materials 

 for forming dense tissue, there will not take place a propor- 

 tionate strengthening of the parts most strained ; and these 

 parts will give way. This happens in rickets. But this 

 having happened, there goes on what, in teleological language, 

 we call a remedial process. Supposing the bone to be one 

 commonly affected — a femur ; and supposing a permanent 

 bend to have been caused in it by the weight of the bod}- ; 

 the subsequent result is an unusual deposition of cartilaginous 

 and osseous matter on the concave side of the bone. If the 

 bone is represented by a strung bow, then the deposit occurs 

 at the part represented by the space between the bow and 

 the string. And thus occurring where its resistance is most 

 effective, it increases until the approximately-straight piece 

 of bone formed within the arc, has become strong enough to 

 bear the pressure without appreciably yielding. jN"ow 



this direct adaptation, seeming so like a special provision, 

 and furnishing so remarkable an instance of what, in medical 

 but unscientific language, is called the vis medicatrix naturae, 

 is simply a result of the above-described mechanical actions 

 and re- actions, going on under the exceptional conditions. 

 Each time such a bent bone is subject to a force which again 



