GROWTH OF BONES. 73 



the bones are quickly coloured by it; when the madder is 

 withheld, the bones become again white; and that the first 

 appearance of the restoration of the latter is manifested by a 

 white lamina being deposited on their surface. The madder, 

 under such circumstances, is a long time in getting out of the 

 bones. I fed a young pig for one month on it, mixed with 

 other food. At the expiration of the succeeding five months, 

 the animal, having grown very considerably, was killed. The 

 interior lamince of all the bones continued to be deeply tinged, 

 while their surface from the deposite of new bone had become 

 white. From this it would appear that deposite is a very per- 

 manent thing in bones : it, of course, must prevail much over 

 absorption, else their growth would be arrested. 



At the same time that the periphery of each bone is increas- 

 ing in its dimensions, the medullary canal is also augmenting : 

 this arises from an absorption going on internally, while the 

 deposite is making externally. Duhamel* proved this by a cu- 

 rious experiment. He surrounded a cylindrical bone of a 

 young animal with a metallic ring; on killing the animal some 

 time afterwards, he found the ring covered externally by a se- 

 cretion of bone,f owing to the growth of the latter, and the 

 medullary canal as large as the ring itself. Notwithstanding 

 the obvious conclusion from this experiment, he made the mis- 

 take of supposing that the bone had enlarged by expansion, and 

 not by a deposite externally with an absorption internally. 



As the individual advances in life, the cylindrical canal, in 

 the centre of the long bones, continues to enlarge in size by the 

 internal absorption : so that the parietes of the bones, which in 

 early life were much thicker than the canal, and in the adult 

 about the same diameter, become exceedingly thin in old age; 

 resembling thereby a stalk of Indian corn, with the pith scoop- 

 ed out.J The cells of the cellular structure in the several 

 bones also enlarge, whereby the whole weight of the bones is 

 much decreased in the very aged. In the parietes of the cra- 



* Mem. de 1'Acad. Roy. des Sciences, an. 1739-41-43-46. 



t If a string be tied around a growing tree, the same thing takes place, and it 

 is finally shut up in the ligneous part. 



t There are several examples of this in the Anatomical Museum. More rarely 

 the reverse takes place, and the cavity is filled up : of this there are also speci- 

 mens. 



VOL. I.-7 



