ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 109 



of position was due to the recession and shrinkage of the anterior cornu, owing to the 

 diminution in the number of its large motor cells which takes place here. Another 

 feature which characterised these cells — a feature which led to this special investigation 

 —was this, viz., that they were not found in each of the successive serial sections. It 

 was noted that they would suddenly appear as a small group of two or three cells, 

 and that in succeeding sections they rapidly rose to a maximum. They then almost as 

 rapidly diminished in number, and thereafter disappeared entirely from the field 

 throughout a varying number of sections. This phenomenon repeated itself eight or 

 nine times in the first dorsal segment. As the lower end of this segment was approached, 

 the groups became larger and the intervals between them shorter. On tracing the 

 groups downwards into the lower part of the first and through the second dorsal segment, 

 it was evident that the cells forming them were the same as those which are there 

 recognised as the intermedio-lateral tract. The examination of the eighth cervical and 

 first dorsal segments of a second, and of corresponding segments of a third cord 

 demonstrated that this arrangement of the cells in groups separated from each other 

 by distinct intervals was a constant phenomenon, and not an individual peculiarity of 

 the cord first examined. The question then presented itself — Was this arrangement of 

 the cells in groups limited to the two segments in question (C. 8 and D. 1), or did it 

 extend throughout the whole of the length of the intermedio-lateral tract, and if so, 

 was there, as had been established in the case of the motor cells in the cervical and 

 lumbo- sacral regions, any grouping of the cells which might be regarded as charac- 

 teristic of each segment in which it was found ? In order to determine these points the 

 third cord was examined from the upper part of the cervical enlargement to its lower 

 extremity. This cord, obtained from an individual presumably free from any disease 

 of the nervous system, was hardened in formalin and divided into root segments accord- 

 ing to the manner employed in preparing the sections for my " Topographical Atlas of 

 the Spinal Cord," sections as nearly as possible at right angles to the median plane of 

 the cord being made below the lowest fibres of each nerve root. The segments so 

 obtained were further hardened in alcohol, embedded in celloidin, and divided into serial 

 sections of uniform thickness. The sections were stained with toluidin blue or with 

 Unna's polychrome blue, with Ford Robertson's precautions to prevent decolorisation.* 

 Special means were taken to ensure that the corresponding sides of each section had a 

 corresponding position on the slide, so that on this ground there should be no error in 

 the enumeration of the cells on either side, or in comparison of those of one side with 

 those of the other. Some 7000 sections in all were examined. Of these more than 

 5000 contained cells of the intermedio-lateral tract. These cells, as found on both sides 

 of the cord, were carefully counted independently by four different observers, t The 



* This group of stains is specially suitable, as it singles out the nerve cells and throws them into such relief that 

 they are more easily enumerated than if stained by #,ny other method. 



t I take this opportunity of acknowledging my indebtedness to Dr Macfie Campbell, Carnegie Research Scholar, 

 for assistance in preparing the sections and enumerating the cells ; to Dr Harvey Pirie, B.Sc, for assistance in 

 enumerating cells ; and to my son, A. Ninian Bruce, for making the drawings for the figures 1-24. 



