STRUCTURE OF THE BONES. 17 



[The cellular structure of bones is attended with several 

 important advantages. In the cylindrical bones it gives great 

 additional strength, by increasing their diameter, without adding 

 to their weight ; for by swelling out their articular extremities, 

 it produces much greater security of the joints, by obviating the 

 tendency to dislocation, and rendering their movements more 

 steady. A simple experiment will satisfy any one that the 

 increase of volume in the extremities of the long bones, is not 

 attended with an increase of osseous matter ; for in the dried 

 bone, the section of an inch from the centre gill weigh as much 

 as the same length from the extremities, notwithstanding the 

 greater size of the latter. Dr. Physick has pointed out another 

 very important advantage of the cellular structure of bones, 

 besides those of its making them nearly as strong as if they 

 were solid, and at the same time diminishing what otherwise 

 would have been a weight too oppressive for the muscular 

 powers. He thinks that thereby the concussion of the brain, 

 and of the other viscera is frequently prevented ; and in nearly 

 all cases diminished, in falls and in blows. He illustrates the 

 position by showing, first, the concussion which takes place 

 through a series of ivory balls suspended by threads ; if one be 

 drawn to some distance from the others, and allowed to impel 

 them by falling. The momentum in this case impels the ball at 

 the farther end of the row, almost to the distance from which 

 the first one fell. But if a ball of the same size, composed of 

 the cellular structure of bone, be substituted for one of the ivory 

 balls, and the experiment be repeated, the momentum of the 

 first ball is lost almost entirely in the cellular structure of the 

 substitute ; particularly if the latter be well soaked previously in 

 water, so as to give it a condition in point of moisture allied to 

 the living state. Adopting this experiment as demonstrative of 

 the fact, Dr. Physick asserts, that in falls from an eminence 

 upon the feet, the percussion, by the time it has passed through 

 the cellular structure of the foot, leg, thigh, vertebral column 

 and the condyles of the occiput, is very much diminished in 

 force, and carries much less impulse upon the brain. Again, in 

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