599 
1907-8.] Middle Cells of Grey Matter of Spinal Cord. 
into root segments by cutting transversely just below the lowest fibre of 
each nerve root. The segments were embedded in paraffin and each cut 
into serial sections ; the sections were then stained with Giemsa’s stain 
(azure blue and eosin). Special means were taken to see that each segment 
was cut and mounted so that the sections were numbered serially from 
above downwards, and that there was no confusion between right and left 
sides. There were in all nearly 16,000 sections. At first, when the 
possibility of the middle cells having a segmented arrangement was before 
me, I attempted to enumerate them, with the idea of representing the 
numbers graphically, but it soon became evident that no such segmented 
C. = Central area. 
Ant. Anterior central area in the base of the 
anterior horn. 
Para. Para-central area. 
Ap. Apical or lateral horn area. 
C.C. Clarke’s column area. 
Post. Post-central area. 
R. Reticular area and area of the formatio 
reticularis. 
Basal. Posterior basal area. 
character existed ; and further, that the task of counting all the cells was 
too herculean to attempt. I therefore contented myself with noting the 
position and arrangement of the middle cells throughout the whole series 
of sections, summing up the results for each 25 as I went along, and again 
for each segment. By this method, I consider, a very accurate idea of 
their distribution has been obtained. 
Some difficulty was felt with regard to nomenclature and division of 
the grey matter into areas. Waldeyer recognises three regions of the grey 
matter : a free anterior horn, a middle region, and a free posterior horn. 
The middle region is defined as including the central canal with trans- 
verse commissures, the lateral horn, the region of the middle cells, and 
Clarke’s column. Everything in front is the free anterior horn ; everything 
