286 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



that in consequence of this irritation the cellules trans- 

 form themselves into osteoclasts, and acquire a new 

 power, that of absorbing bone. The function will 

 cease as soon as the teeth are formed, by the termina- 

 tion of pressure, and then the formative action of the 

 cellules adjacent to the bone will repair it as a conse- 

 quence of a retransformation of these elements into 

 osteoblasts. 



"I will not push further this first attempt at an 

 explanation of the normal absorption of bone, but I 

 content myself with observing, that in any case, pres- 

 sure exercised by the soft parts counts for much in this 

 phenomenon. Who does not remember in the face of 

 these facts, numerous cases of pathological absorption 

 of bone due to aneurisms, tumors, and hypertrophied 

 organs? Who will not admit the great effect of the 

 disappearance or arrest of development of organs on 

 the size of their osseous surroundings \ as Fick, for- 

 merly professor of anatomy at Marburg, has shown to 

 take place in the orbit after the extirpation of the eye? 

 It is possible to go a step further in the proposition, 

 that external pressure has much to do with absorp- 

 tion. Thus the growth of the brain and spinal cord 

 produce the resorption seen in the interior of the skull 

 and of the spinal canal ; that of the eye and of the 

 nasal mucosa, and of the cranial vessels and nerves, 

 have resulted in the enlargement of their cavities ; and 

 in the case of foramina, in their wider expansion. . . . 

 The medullary cavities of bones are produced in the 

 process of growth by the corrosive activity of osteo- 

 clasts." 



It is then pressure which produces the excavations 

 which form new cotyli m the construction of new ar- 

 ticulations due to dislocations. By such excavations 



