Hardesty, spinal Ganglion Cells. 23 



In counting the ganglion cells an application of the net method 

 had to be used exclusively. Here all the sections involving the gang- 

 lion had to be gone over and photography was practically out of the 

 question. Therefore, the problem had to be approached in another 

 way. It was first determined that but few of even the very smallest 

 of the spinal ganglion cells have a diameter of less than 9 /<, and 

 further that 9 fi sections were thin enough to allow the light to pass 

 through sufficiently to distinguish the intervening structures of the 

 cell. For this reason 9 n was chosen as a convenient thickness. On the 

 other hand, however, some of the largest cells of the ganglia may ex- 

 tend through as many as seven consecutive sections of this thickness. 

 To obviate the danger of double counting, a procedure was adopted 

 throughout, which I think was first described by Gaule and Lewin 

 {'96) in their enumerations of the spinal ganglion cells of the rabbit. 

 This consisted in counting only the nucleoli in the sections. As with 

 them, the question of course arose as to the danger of double count- 

 ing because 'of the existence of double nucleoli. In counting the cells 

 in several of the ganglia here dealt with. I kept a record of the dou- 

 ble nucleoli appearing in the sections and found that two nucleoli oc- 

 curred in the same cell at an average of about 5 cells in 1000 or at the 

 rate of about one-fifth of i % . Cells in which they were observed were 

 usually among the smaller cells of the ganglia. They, of course, were 

 not counted twice. Remembering that these double nucleoli were 

 seen in sections of 9 yu, and that double nucleoli in a nucleus are never 

 separated as much as 9 /< from each other, and further, that certainly 

 not more than half of such cases existing have their nucleoli separated 

 in the plane perpendicular to the plane of the knife in sectioning so 

 that the knife may pass between them, it is therefore evident that the 

 number of cells counted twice because of double nucleoli is probably less 

 than one-fifth oi \%. The proabilities of double counting due to nuclei 

 being cut in half by the knife and thus counted in the two sections, 

 are also such as need only be considered in questions of the most abso- 

 lute accuracy. In exceedingly few cases did appearances and com- 

 parison of the consecutive sections indicate this had happened. None 

 of the conclusions drawn in this paper would be materially affected by 

 an acknowledged error of one-fifth of i % . 



The number of cells counted in each section was' recorded sepa- 

 rately and not till all the sections of a ganglion had been counted were 

 these numbers added to obtain the total number of cells in the gang- 

 lion. The larger ganglia often involved as many as 125 sectionR. In 

 no case was the relation between the number of ganghon cells and the 



