Ranson, Degeneration m Spinal Nerves. 277 



ganglion cells has been described in a number of papers from this 

 laboratory, and especially in the publications of Hardesty. In 

 counting fibers the net method was used. The entire ventral 

 root and each of the fasciculi of the dorsal root and mixed nerve v^ere, 

 with few exceptions, small enough to come within one field of the 

 microscope. The field was divided into small squares by a net 

 micrometer placed in the ocular. The fibers in each square were 

 counted in the order of the squares until the enumeration of the 

 entire root or fasciculus was completed. The counting was done 

 automatically by pressing the lever of a counting machine once 

 for each fiber and reading off the final number from the face of 

 instrument. In the few cases in which it was necessary to shift 

 the preparation during the enumeration of a root or fasciculus, 

 a straight line joining two prominent pomts was regarded as the 

 limit between the two fields, and the position of this line was 

 indicated by a line of the micrometer made to lie across the two 

 points. 



The enumeration of the nerve cells in the serial sections of the 

 spinal ganglia was somewhat more difficult, since several suc- 

 cessive sections may contain parts of the same cell. The diffi- 

 culty was avoided by counting in a given section only those cells 

 which showed nucleoli. These structures are small enough to 

 escape division by the knife and so to lie, in the vast majority of 

 the cases, within the plane of a single section. In most cases each 

 cell has but one nucleolus, in rare instances there are two; but the 

 presence of a pair would lead to error only in those extremely rare 

 instances when the knife passed between them in such a way as to 

 give a nucleolus to each of two sections of the same cell. Har- 

 desty estimates that this would not o-ive an error of more than 

 0.2 per cent. The cells with nucleoli were enumerated with the 

 aid of the counting machine in each section of the series; the sum 

 of the numbers for the individual sections gave the total for the 

 ganglion. Since a section of the ganglion could not all be brought 

 into the field at once, it was necessary to use a mechanical stage 

 which permitted a ready shifting of the preparation. In the spinal 

 ganglion the different portions of the section are so character- 

 istic that one does much better to dispense with the net micrometer 

 and depend entirely upon the natural markings, which are ade- 

 quate to prevent confusion as to what part of the section has been 

 counted. 



