354 MR. J. LOCKHART CLARKE ON CERTAIN FUNCTIONS OF THE SPINAL 
The results obtained from the experiments of Stilling abore described are 
involved in much obscurity ; for in addition to other reasons, it would seem extremely 
difficult, if not impossible, to avoid leaving a portion of the anterior columns undi- 
vided.~that portion, namely, which is situated internal to the anterior grey sub- 
stance But even if they tended to show that the power of volition is not transmitted 
by these columns, they by no means prove it to be communicated by the grey sub- 
stance, since a deep incision into the latter would divide not only many fibres of the 
anterior roots extending upwards, but a portion also of the lateral white columns 
into which these roots are prolonged. . ^ -i ^ 
That the grey substance of the chord does transmit impressions from one side to 
the other, has been fully proved by the experiments rf Van Been and Stilling ; and 
the means by which the communication is effected is satisfactorily explaine > e 
structure of the transverse commissure described by both Stilling and mjse . 
believe however, that the fibres of this commissure do not form a distinct set con- 
necting the grey substance of one side with that of the other, but that they are all 
continuous with the roots of the nerves and the white columnsf . 
From certain facts, then, described hi this commnnication, it would appear that 
the white columns are mainly constituted of fibres derived from both roots of the 
nerves It is true that the processes of some of the vesicles situated near the ma'f “ 
of the grey substance may be seen to extend into these columns, with fibres of which 
they perhaps are continuous ; and it is not improbable that others more deeph seated 
may have the same connection. But if there be, as some physiologists believe, a 
* The structure immediately surrounding the spinal canal is described by Stilling as is circular commecv 
composed of line grey fibres. By R.Msir it is spoken of as the couia.isc.ra gclalinosa. and ^ a cont.nu.uon 
tL sutslaulia hLosa of the posterior grey suhstance. KoLLinea, who declares that Un. sUuc u„ was 
mistaken by Stil'.ng for a spinal canal-the existence of which he denies-also considers it as a peculiar kmd 
of vesicular substance, enclosing a central nucleus, (yraaer cenlralcr Korn) and which ^ “ 
grisea cenlralis. I. appears, however, as described in my former commumcauon to cons«t “J “ ■ 
rf fine fibrous tissue surrounding and supporting the columnar epithelium which forms the w^ -P “ 
canal. The existence of this canal is unquestionable ; but in the human chor it is o en c o.e , , i 
““f by lateral pressure, to a mere line ; and around this the columnar epithelium is arranged in the term of 
an ellipse, which Kollikee appears to have mistaken for a double nucleus. , . ,i,- 
t There seems to be a great correspondence in the fibrous arrangement between the grey substance of the 
spinal chord and the chiasma of the optic nerves. In a few transparent preparations that I have ma « ° ' 
latter:, the structure first pointed out by Mato is very clearly discerned ; but the course of the fibres is found 
to be stm mote intricate. There is a remarkable circumstance that I have observed, and which I do not lecol- 
lect to have seen recorded, respecting the cross action of the optic nerves. After 'ookmg through the micro- 
scope if the eye employed be directed to other objects, it must be weU known that the is found 
be unimpaired, although the colour is rendered darker than natural, in direct proportion to the previous stun^u 
„ light 1 but if the same objects be viewed by the other eye which has not been employed at he microscope, 
Ive inlariably noticed that an opposite effect is produced, and in the same 
natural, but the definition is more or less impaired. It may be stated then as a law. t a , y cose 
loith magnifying gLcs. under the stmulus of a strong light, -in the eye employed, the perception of colour, S.1 
Tde/nfpZ, is affected, chide in the opposite eye, the defnin, pouter, hut not the perception of colour, m 
impaired, and in a direct and equal ratio. 
