52 Wisconsin Academy of Sciences^ Arts and Letters. 



elements or not, the process will be exceedingly slow and. 

 wearisome, and the result thoroughly untrustworthy. Since 

 our methods of discriminating staining are yet far from 

 perfect, the structures capable of counting are still few. Dr. 

 Gaule, of the Physiological Institute at Leipsic, under whose 

 direction this paper was worked out, called my attention to 

 two structures which filled both the above conditions, and 

 which were of great interest. These were the meduUated 

 nerve-fibres of the anterior roots of the spinal nerves, and 

 the large ganglion cells of the anterior horn of the gray 

 matter of the spinal cord. The enumeration was made upon 

 the frog, the most favorable animal, both because of its small 

 size and because of its importance in experimental physi- 

 ology. 



The value of such enumerations as the following depends, 

 of course, entirely upon their accuracy. I have attempted in 

 every way to assure myself of the reliability of my results. 

 The close correspondence of the number of cells found on 

 right and left sides, seems to me the clearest proof of the 

 accuracy of the counting. 



The numbers of the elements which I have determined 

 lead to certain conclusions, apart from any theoretical con- 

 siderations. 1. The frog has an equal number of cells in 

 the anterior horn of the spinal cord, and of fibres in the 

 anterior roots of the nerves. Each motor cell, then, corre- 

 sponds to a motor fibre. 3. There is a general correspond- 

 ence between the number of cells in any region of the spinal 

 cord and of fibres entering that region. When an individ- 

 ual frog shows peculiarities of distribution of fibres to 

 different nerves there is a corresponding peculiarity in the 

 distribution of the motor cells. It is thus probable that the 

 ganglion cell belonging to a particular fibre lies not far from 

 its entrance to the cord. 3. The number of fibres and cells 

 varies with the weight of the frog. Each frog starts with a 

 certain minimum number which is regularly increased with 

 the increase in weight. Hence (a) the fibres and cells must 

 be constructed during the life of the frog; (b) a certain re- 

 lation obtains between the weight of the muscles and the 

 number of the motor fibres and cells. 





