440 ME. J. L. CLAEKE ON THE GEEY SUBSTANCE OE THE SPINAE COED. 
B. Cells of the Gelatinous Substance^ .—Tcie cells of tlie gelatinous substance, in 
regard to size, may be described as («) large, {h) small, and {c) mtermediate. 
(a) The large cells are almost exclusively found amongst the senucncular fibres which 
run within the external border of the substantia gelatinosa, and never extend beyond the 
middle of its depth (fig. 1, Hate XIX., and fig. 47, Hate XXII.). They ai-e more or less 
oval, pyriform, fusiform, crescentic, triangular, or otherwise irregular, and contam distoct 
nuclei. They all give off processes from two to five or six in number. The fusijoi m 
and oval variety are elongated transversely, longitudinaUy, and m planes mtennediate or 
oblique. Sometimes a fusiform ceU tapers at each end^ into a broad process, whic^ 
attenuates in its course, and either remains single or subdmdes into two or more ; or it 
bifurcates at once into two processes at each extremity or only at one. In a Hansverse 
section of the cord, some of these processes appear to terminate in one or more ot the 
semicircular or marginal fibres; some run backwards through the postenor columns, or 
forwards across the gelatinous substance; others pursue a longitudinal coui’se wuth the 
■fibres of the gelatinous substance, or along the verge of the posterior columns. From a 
cell of another shape three or more processes may be seen to extend in different -ec- 
tions--backwards, forwards, laterally, obliquely, or longitudinally. Frequently a in- 
angular cell, resting on the verge of the gelatinous substance, sends a process nght aM 
left, and a third through the posterior column along the side of a bundle of the pos c- 
enter the grey substance in a more or less longitudinal dh-ection, or .ith various degrees of ohliquiU’’ 
And in second communication, Philosophical Transactions, 1853, p. 353, it is stated, « I beheve that 
they (the longitudinal fibres of the gelatinous substance) are aU derived from the fine fibres ot the pos tiioi 
roots ” which must therefore cross the gelatinous substance in an oblique dii-ection. ^ 
* The cells of the gelatinous substance have been described by Koluikee, Scheodee vax dee Kolk, 
and by STiEiixe in his late work. In my first communication I only incidentally mentioned them in the 
following passage : “ All (the nerve-cells of the grey substance), except those peculiar to the gelatmous su - 
stance, have remarkably delicate processes issuing from their sides.” Upon this passage ta -es 
the opportunity of remarking, that by my peculiar method of preparation the sections are rendered too 
transparent, so that the finer elementary structures escape observation. Tins objection is Dutboiit su&oient 
foundation. In the first place, I described the gelatinous substance, as I then stated, from examination of 
i\i& fresh cord, treated with acetic acid, and not by means of my “peculiar method” of preparation, which, 
however, shows the cells and processes in the most perfect manner ; secondly, to see these preparations to 
advantage, the illumination must be adapted to their degrees of transparency. But they may be made of all 
degrees of transparency and of thickness up to the one-twelfth of an inch. If Sxiedixg has given but a 
hasty trial to this method and only messed with a little tui’pentine and Canada balsam, he is not prepared 
to offer an opinion worth notice. I may add that the few of my prepai-ations that have found their way to 
the Continent are some of the first that I made, and are very inferior to those I have smce made, especially 
by my modified method. The great thickness, also, of some of these preparations renders them exceed- 
ingly valuable for tracing the course of fibres, which must ofteu be mevitably cut across in the very tbm 
sections required by other methods. This is evident m Stilling’s large waU-diagiam, where the grey sub- 
stance particularly of the cervix cornu posterioris, appears chopped up like chafl ; so that it is impossible 
to form any idea of the destination of the fibres. It may not be out of place to state that all the observa- 
tions described in this communication have been carefuUy repeated on sections of the cord hardened simply 
in chromic acid, and without further preparation. 
