Donaldson and Hoke, Medullary Sheath. 3 



treatment, and this view is shared by a number of other ob- 

 servers who have studied this question. The method employed 

 in this investiijation was practically the same as that used by 



BOVERI. 



Speaking generally, it may be said that mistreatment tends 

 to cause a swelling of the medullated fiber (in i % osmic acid) 

 in which the sheath becomes somewhat more swollen than the 

 axis. The most reliable measurements, therefore, are those 

 made on nerves which have suffered the least mechanical dam- 

 age. 



To determine whether our method of treatment produced 

 permanent alteration in the size of the nerves used, a series of 

 observations was made upon the eighth, ninth and tenth spinal 

 nerves running free along the dorsal wall ot the body cavity of 

 the frog, and also on the sciatic nerves of the white rat. 



The nerves were laid bare and a bristle bent in the 

 form of the letter U, exerting a tension of .25 to .40 grams, 

 according to the size of the nerve, was rapidly tied to either 

 end of the nerve. In this way about one centimeter of nerve was 

 included between the ends of the bristle. The nerve thus prepared 

 was then removed and before putting it in any fluid its diameter 

 was carefully measured under the microscope. It was then 

 placed for twenty-four hours in a shallow cell containing osmic 

 acid. The subsequent treatment was exactly similar to that 

 given under the paragraph on technique. Bristle and attached 

 nerve were finally mounted in colophonium and the diameter 

 again carefully measured. 



The results of these observations are presented in Table I 

 for the Frog and Table II for the Rat. 



The column on the left gives the diameter in [x of the fresh 

 nerves with the bri.sile attached. On the right is given the di- 

 ameters in n while the nerves are in colophonium, after com- 

 plete treatment by the osmic acid method as described above. 

 In Table I, the middle column introduces the diameter of the 

 nerves after having been in osmic acid twenty-four hours. The 

 final number at the foot of each column gives the square of the 

 average radius. This number, when multiplied by /r would 



