LAWS OF BONE ARCHITECTURE 221 



pears entirely rational to consider the effect to be the same as 

 a load equal to the body weif2;lit a])phed suddenly to the foot. 

 The mechanical effect of a suddenly applied load is exactly 

 double that of a static (stationary) load of the same amount. 

 That is, the stresses produced in a structure by a load, of say 

 100 pounds, suddenly applied, will be as great as those produced 

 by a static load of 200 pounds. 



Obviously the stresses in the femur due to running wil be 

 greater than those due to walking. In running or in walking 

 the actual weight carried by the head of the femur which is 

 loaded, is the body weight less the weight of the loaded leg it- 

 self (20 per cent of the body weight) or a load equal to 80 per 

 cent of the body weight. The effect of running is to produce 

 stresses in the femur equal to those produced by twice as great 

 a static load as the weight boine on the femur-head. Hence 

 the stresses in the femur due to running are those produced by 

 a static load of 160 per cent of the body weight. This will be 

 considered in later paragraphs discussing the factor of safety 

 in the fenun fp. 274). 



Material studied 



A preliminary study of the architecture of the femur and 

 other bones was made, utilizing femurs and other material from 

 the dissecting-room. This work yielded considerable informa- 

 tion as to the planes in which sections should be cut in order 

 to show most clearly the essentials of the inner architecture 

 of the bones studied. Some 25 or more femurs were studied in 

 this manner, but as nothing definite was known regarding the 

 subjects, state of health at death, body weight, etc., no detailed 

 quantitative analysis of such specimens was undertaken. 



If quantitative relationships are to be established between 

 bone structure and body weight, the specimens analyzed must 

 be those which represent conditions that obtain in the normal, 

 healthy individuals. The femurs finally obtained for such a 

 study were those of an active, healthy American negro who 

 had been killed accidentally. This subject was a large-framed, 

 well-nourished laborer, about 35 years old, six feet in height 



