'24 



ininutc structtiic of a spinal ;,^aiij,diim. Wliat is tin' 

 patli of II nervo impulse througli tlie jijaii^linii ? Tlic 

 supposition has been, since Ranvier's work, tliat a HImt 

 enters a spinal ganglion, unites with one of its cells })y 

 a "T" process, anil passes out in the opposite direc- 

 tion. This supposition finds support in the way a 

 nerve degenerates when separated from the ganglion, 

 and in the fact that the same number of fibers enter a 

 ganglion as leave it.' It is also supported by Birge's- 

 work, in which he finds a single ganglion cell in the 

 anterior horn of the frog's spinal cord for each nerve 

 fiber in the anterior root. If this relation holds for the 

 cells and fibers of the spinal ganglion, we should evi- 

 dently find a cell in the ganglion for each fiber in the 

 posterior root. Expecting to demonstrate this. Dr. 

 Nelson,* working under the direction of Birge in the 

 University of Wisconsin, counted the fibers in the 

 posterior root and the cells in the corresponding gang- 

 lion. The work was done on the frog, and in all about 

 ten ganglia were counted. Nelson found, allowing 

 3—1: per cent for error in counting, two ganglion cells 

 for every fiber in the root. This counting has been 

 repeated for two ganglia by myself, and for one more 

 by still another observer. Our figures are as follows : 



No. nbers No. of colls 



In root. intrangUon. 



t^eventh ganglion, right side, 1128 2767 



Eighth " left " 1811 .541f! 



Seventh " left " 1340(T.'8count)1364(my coiiiiU445<i(T.)t 



' Ueber den Ban der Spinalganglien. M. Hall. Wiener Acad. 

 Sitzungsber. LXXII, 3, p. 31-37. 



■Die Zahl der Nervenfasern und der motorischen Ganglienzcllcii 

 im Kiickenmark dcs Krosohes. E. A. Birge. Archiv fiir Anat. und 

 Pliys. 1882, Physiol. Abth. p. 435. 



'The above is inserted by the courtesy of Dr. Nelson. His notes 

 of the work were destroyed in the burning of Science Hall, Madison, 

 Wisconsin. 



f The most careful count of all, done under magnifying power of 

 Leitz, Obj. 7, Oc. 3 ( = 600 diameters) for flbers, and'Obj. 7, Oc. 1 

 = 325 diameters for cells. 



