TEXTURE OF BONES. 55 



tionately to their weight, as one inch or any other given section 

 of the compact part weighs very nearly the same with a section 

 of equal length from the cellular extremities. The swelling at 

 the ends of the bones adds much to the safety of their articular 

 union, as the extent of the surfaces is thereby much increased, 

 and, consequently, they are less liable to displacement. The cy- 

 lindrical and the cellular cavities, thus formed in the long bones, 

 by increasing the volume of the latter, add greatly to their 

 strength beyond what would have occurred, had the same quan- 

 tity of material been solid. The late Dr. P. S. Physick demon- 

 strated this most satisfactorily by a scroll of paper, which, on 

 being rolled up successively, into cylinders of various sizes, has, 

 like a lever, its power of sustaining lateral pressure on one of its 

 extremities, continually increased as its volume or diameter is 

 augmented, until the latter reaches a certain extent. The same 

 highly distinguished teacher also pointed out another very im- 

 portant advantage of the cellular structure. It is that of serving 

 to diminish, and in many cases to prevent concussion of the 

 brain, and of the other viscera, in falls and in blows. The opi- 

 nion was verified by his demonstrating the momentum, which is 

 communicated through a series of five ivory balls suspended by 

 threads, when one of them is withdrawn from the others, and 

 allowed to impel them by its fall. This momentum is so com- 

 pletely transmitted through the series, that the ball at the far- 

 thest end is impelled almost to the distance, from which the first 

 one fell. This familiar experiment, used as a preliminary test 

 to the accuracy of his views, was immediately succeeded by his 

 substituting for the middle one of ivory, a ball made of the cel- 

 lular structure of bone. The same degree of impulsion now 

 communicated at one end of the series, is almost lost, or rather 

 neutralized, in the meanderings of the cellular structure of the 

 substitute; and particularly if the latter be previously filled with 

 tallow or well soaked in water, so as to bring it to a condition 

 of elasticity resembling the living state. 



In persons of advanced age, the marrow of the bones becomes 

 more abundant, and their parietes thinner; and we also observe 

 then, that the bones break more readily, and are more crum- 

 bling, rotten, or soft, than during the anterior periods of life. 

 In women, after the critical period is passed, these traits are 

 especially developed, and the compact centres of the long bones 



