22S JOHN C. KOCH 



Of the 75 transverse sections into which the f(Mmir was cut as 

 just described, the follownig sections were analyzed in detail 

 and are shown in Plates 1 to 5: 2, 4, 6, 8, 10 12, 14, 16, 18, 20, 

 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 66, 68, 70, 72, and 75. 

 The positions of these sections are indicated by these numbers 

 on the various drawings and diagrams, which also indicate the 

 distances in ^-inch units from the upper extremity of the femur 

 to the corresponding sections, as measured along the longitu- 

 dinal axis. The detailed study of these sections will now be 

 taken up. 



2. Center of gravity. The first step in analyzing these trans- 

 verse sections is the accurate location of the center of gravity 

 of each section. The true longitudinal axis is the line joining in 

 succession the centers of gravity of the transverse sections. 



The center of gravity of each section was located by the 

 method of suspension. The transverse section whose center of 

 gravity is to be determined is suspended from any point and the 

 direction of the suspending thread is carefully marked on the 

 section. The operation is then repeated, suspending the sec- 

 tion from any other point, and marking on the section the di- 

 rection of the suspending thread. The center of gravity of the 

 section lies at the intersection of the two liiies whose directions 

 have been marked on the section. A third line may be found in 

 a similar manner, and this should pass through the point of in- 

 tersection of the other two lines, thus checking the accuracy of 

 the determination. Every section has been twice checked in 

 this manner. In each of the sections shown in Plates 1-5 the 

 position of the center of gravity is at the intersection of the two 

 axial lines A- A and B~B. 



3. Neutral axis and neutral surface. As has been more fully 

 explained under the same heading in Part II, the neutral sur- 

 face of a beam is that surface or plane on which there is neither 

 compressive nor tensile stress. This surface passes through the 

 center of gravity of the section considered. This surface is 

 approximately at right angles to the vertical plane passing 

 through the head and neck of the femur when the body is in 

 the normal erect position 'of 'attention.' 



