686 'Journal of Comparative Neurology and Psychology. 



The findings in the second paper give the number of meduUated 

 nerve fibers in the main trunks of the two hind legs of one frog at 

 the successive levels of the thigh, the shank, and the foot, and the 

 numbers in the primary branches to the thigh and the shank. From 

 these data there was determined for each segment of the leg, the 

 number of medullated nerve fibers destined to innervate the skin, 

 the number for the muscles, and those for the knee and ankle joints. 

 Certain measurements of the diameters of the medullated nerve 

 fibers were also accomplished. 



It was then found desirable to make a further differentiation of 

 the medullated nerve fibers according to their function. To this 

 end an attempt to destroy the efferent medullated nerve fibers by 

 severing the ventral roots of the spinal nerves supplying the hind 

 leg was made in the spring and summer of 1904. In August of 

 that year a successful operation was performed and the life of the 

 frog was maintained for eight months with the expectation that the 

 medullated nerve fibers separated from their perikarya w-ould degen- 

 erate and thus the medullary sheaths would be broken down and 

 be unstained in a preparation treated by the osmic acid method of 

 staining. 



As sterilization of the skin in preparation for the operation was 

 well nigh impossible, the instruments used for the skin incision were 

 discarded and the remainder of the operation performed with sterile 

 instruments kept in sterile distilled water. As has been found 

 advisable in operations upon the central nervous system, antiseptics 

 were avoided. Ether was used for the ansesthetic. The body of the 

 frog was kept cool and moist by pads of wet sterilized cotton. 



A considerable skin incision was made in the dorsal midline and 

 the flaps reflected. The transverse processes of the vertebrse with 

 the surrounding tissues were severed completely on one side, and 

 partially upon the second side, thus forming a flap of bone and 

 muscle which at the close of the operation was replaced to form a 

 protection for the spinal cord. The constant oozing into the spinal 

 canal with consequent obscuring of the field of operation was met 

 by the use of capillary drainage formed by a rolled thread of absorb- 

 ent cotton. 



