THE CONDITION OF OLD AGE n 



a spongy structure, bits of bone bound together in 

 many different directions, as are the spicules or fibres 

 in a sponge, and by being bound so together they 

 unite lightness with strength. As you know, a col- 

 umn of metal, if hollow, is stronger than the same 

 amount of metal in the form of a rod. So with the 

 bones. If they have this spongy structure, if their 

 interiors are full of little cavities with intervening 

 spicules acting as braces in every direction, then they 

 acquire great strength with little material (Fig. 5). 

 Now in the old much of the internal spongy structure 

 is dissolved away and there is left (Fig. 6) barely 

 more than an external shell. Partly on this condition 

 depends the greater liability of the bones in the old 

 person to break. If we examine the muscles we see 

 that they have become less in volume, and when we 

 apply the microscope to them we see that the single 

 fibres on which the strength of the muscles depends 

 have become smaller in size and fewer in number. 1 

 Professor B. Morpurgo 2 by an ingenious experiment 

 has demonstrated that exercise increases the size of 

 the muscles by increasing the size of the single fibres. 

 Exercise produces a true physiological hypertrophy 

 but no increase in the number of the fibres. This 

 important discovery suggests the idea that senile 

 muscular diminution is due chiefly if not exclusively 



1 This statement is the one currently accepted but I have found, as yet, no 

 exact investigation upon the relative size and number of the muscle fibres in 

 old persons. 



2 B. Morpurgo, " Ueber Activitats-hypertrophie der wilkurlichen Muskeln," 

 Vir chow's Arch. Pathol., Bd. cl., 522-554(1897). 



