212 JOHN C. KOCH 



stnited that they act as other elastic materials (wood, steel, etc.) 

 and therefore the same laws of mechanics may be applied to 

 their study and the determination of their strength. 



Raiiber ('7()) has made very complete studies of the behavior 

 of sections of bone taken from various parts of the skeleton, by 

 testing them in various ways to determine the ultimate stresses 

 that small sections actually develop. 



1. Specific gravity. Hiilsen ('98) gives the specific gravity of 

 fresh, compact human bone from 1.507 to 2.024. 



Rauber gives the specific gravity of fresh compact bone of 

 femur and tibia as follows: 



Man 30 years old 1 . 901 



Woman 56 years old 1 . 825 



Cat 2. 101 



Bullock 2.024 



Calf 1.889 



Domestic hog 1 .965 



Wild hog 2 .060 



He also gives the specific gravity of fresh spongy bone from 

 the human femur head, 1.197. 



I have made experiments carefully on sections of compact bone 

 from the shaft of human femurs as found in the dissecting room, 

 which gave variations from 1.915 to 1.990 in a series of 17 speci- 

 mens, with an average of 1.955. These figures are based on 

 bone from which the marrow, blood and other non-osseous ma- 

 terial had been removed by boiling and then air drying for a 

 number of days. 



2. Tensile strength. The ultimate tensile strength of fresh, 

 normal, compact, human bone is variable between 9.25 and 

 12.41 kilograms per square millimeter, or in English measure 

 from 13,000 to 17,700 pounds per square inch, according to 

 Rauber's tests. Hiilsen ('98) gives the ultimate tensile strength 

 of similar bone as 10.40 to 10.56 kilograms per square milli- 

 meter or from 14,750 to 14,980 pounds per square inch. 



3. Compressive strength. The idtimate compressive strength 

 of such compact bone is variable from 12.56 to 16.85 kilograms 

 per square millimeter, or from 18,000 to 24,000 pounds per 

 square inch according to Rauber's tests. Hiilsen gives as the 



