Donaldson and Hoke, Medullary Sheath. 7 



latter is the number desired, it is necessary first to find the 

 square of the radius in the case of each of these ten fibers ; then to 

 take the average of these squares and multiply by n in order to 

 obtain the average area of the fibers. 



TABLE V. 

 The squares of the foregoing radii are as fo Hows : 

 (Radius A + S)« (Radius A)^ 



The average for the squares of the radii in the case of the 

 axis and sheath and of tiie axis alone, must be multiplied by ^ 

 (= 3. 14) to give in square // the areas of the entire fiber and of 

 the axis respectively. In this instance the areas are as follows: 



Areas. 

 Entire Fiber Axis 



154.9 sq. t.1 76.99 sq. u 



The object of this investigation is to determine whether in 

 the cross section of the fiber the area occupied by the ring-like 

 sheath is equal to that of the enclosed axis. 



By hypothesis they should be equal in area, hence in the 

 case of the average entire fiber containing 154.9 ^q- /-< in its sec- 

 tion we should expect to find one-half of this area 1^^= 77-5 



sq. iL in the axis and the other half in the sheath. 



With this ideal area, the area of the axis as observed is 

 compared. Thus: Estimated area of sheath = 77.5 sq. /i. 

 Observed " axis =76. 99 sq./i. 



According to the hypothesis, the area of the axis should 

 equal that of the sheath. The observed area of the axis is seen 

 to be less by o. 5 i sq. //, or using the ideal area of the sheath 



