238 JOHN H. KOCH 



sjiry to ('()nii)uto (ho intensity of (ho horizontal shcnirinji; force 

 a( a number of points in each section of the head and neck of 

 the femur where the shearing forces produce their ]>i'incipal 

 effects. In each of these tr-ansverse sections the coefficients, Q, 

 of tho intensity of the horizontal shearing stress were computed 

 at intervals of i^ inch from the neutral surface of the femur. 

 The horizontal shearing unit-stress at these points is found by 

 nmltiplying the average vertical shearing unit-stress for the 

 section by the coefficient Q, for the given point. 



The method of computing the intensity of the horizontal 

 shear is shown in table 4, which gives the complete calculations 

 in tabular form for transverse section 8. In similar manner, the 

 intensity of the horizontal shearing forces have been computed 

 for the other even-numbered sections from 4 to 18 inclusive. 



Having found the horizontal shearing unit-stresses for the 

 various points in each section, the vertical shearing unit-stresses 

 are also known as they are equal in amount at corresponding 

 points, and differ only in being directed at right angles to the 

 horizontal shears. 



5. The unit-stresses due to the external load. A. Axial unit- 

 stress. The axial unit-stress is the axial load at the section di- 

 vided by the net area of the transverse section. In the sections 

 containing spongy bone the area is expressed in terms of the 

 equivalent area of compact bone. The unit-stresses have been 

 computed for each section by dividing the axial load by the 



TABLE 6 



Analysis of stresses in the normal femur produced by a load of 100 pounds: by 



walking and by running 



In this table there is given, in condensed form the analysis of the stresses produced 

 in successive sections of the normal femur, by a load of 100 pounds applied to the 

 head of the femur in the same direction as the body weight is transmitted. From 

 the data tabulated the maximum unit-stresses {lbs. per sq. in.) at the various 

 sections is computed for the load of 100 pounds. Then by simple proportion, 

 in accordance with the principles of mechanics the maximum stresses at these 

 sections are calculated for a load of 160 pounds and for a load of 320 pounds on 

 the femur, being the approximate load carried by the femur in walking and in 

 running, respectively. The numbers of the sections given in column 1 corre- 

 spond to the numbers of the sections in figure 18 and all other diagrams and tables 

 similarly numbered 



