246 JOHN C. KOCH 



tensile uiiit-stiess ;it the various sections due to the combined 

 action of the axial load and tlie bending moment, while curve 

 5 gives the coi'i-esjionding maximum compressive unit-stresses 

 due to the combined action of the axial load and the bending 

 moment. 



In this figure curves 7 and 6 show the intensity of the maxi- 

 mum compressive and tensile unit-stresses along the femur due 

 to the combined action of the axial load and the bending mo- 

 ment, for a load of 160 pounds ( = 8/10 of body weight) on the 

 femur-head, produced in walking by the subject who weighed 

 200 pounds. 



7. Tlie lines of maximum internal stress. In Part II, 53, the 

 formulas for computing the magnitudes and directions of the 

 maximum and minimum internal stresses were given. The 

 unit-stresses due to axial load, bending moment and hori- 

 zontal and vertical shear having been determined for the vari- 

 ous sections as described above, the formulas mentioned can 

 now be applied to compute the directions and magnitudes of the 

 maximum and minimum internal unit-stresses throughout the 

 femur. 



Distal to section 16 the shearing stresses are quite small 

 (see curve 8, figure 17, giving maximum intensity of horizontal 

 and vertical shearing unit-stresses), and produce no appreci- 

 able effect upon the position of the lines of internal stress. For 

 this reason the lines of maximum internal stress become parallel 

 to the longitudinal axis of the femur below this section. 



In the head and neck of the femur the stresses due to bending 

 moment and vertical and horizontal shear combine to produce 

 maximum and minimum internal stresses at every point in this 

 region. These maximum and minimum stresses act everywhere 

 in directions perpendicular to each other. Where the maximum 

 tensile stress occurs there is also a minimum compressive stress 

 acting at right angles to it: and conversely, wiiere the maximum 

 compressive stress occurs there is a minimum tensile stress at 

 right angles to it. 



As there is an infinite number of points in each transverse 

 section subject to the action of these forces, which vary in in- 



