The Motor Ganglion Cells of the Fray's Spinal Cord. 53 



■ I. Number of Motor Fibres. 



The roots were treated in situ with osmic acid, one per 

 cent., for two to six hours, and imbedded in paraffine. The 

 sections must not be over 1-100 mm. thick, better 1-200 mm., 

 since if the axis of the fibre is not exactly perpendicular to 

 the section the light will not pass through it unless the cyl- 

 inder is very short. If the fibres overlie each other, or if 

 they are so long that their obliquity cuts off the light, rapid 

 and accurate counting is out of the question. 



The counting was performed with an eye-piece micrometer 

 divided into squares. Some counts were made with the 

 camera lucida, marking each fibre by a pencil dot. This 

 was a less accurate method. All nerves were counted twice, 

 and the work was repeated if the difference was over two 

 per cent. 



The results are shown as follows: 



TABLE I. 



Number of frog 



Weight in grammes . . . . 

 Motor fibres on one side. 

 Total motor fibres 



42 



111 



5,734 



11,468 



The total number is reached by doubling the number ob- 

 tained on one side. As will be seen later in the section on 

 ganglion cells the number is the same on the two sides. 



A somewhat regular increase of fibers proportionally to 

 the increase of weight is seen : 



TABLE II. 



Frog 49 



Increase of weight i 



Increase of fibres I 



Fibres per gram, of increase] 



46 



8 



497 



62 



41 



21.5 



1,064 



50 



36 

 61.5 



2,582 

 42 



40 



65.5 



3,508 



53 



43 



85.5 



4.020 



47 



42 

 109.5 

 5,484 



50 



From this table it becomes possible to compute a priori 

 the approximate number of fibres, at least for Rana escu- 

 lenta. The addition of fifty fibres for each gramme in 

 weight to the fixed number G,000 will come near the required 

 result. The female frogs must be weighed without ovaries. 



