352 MR. J. LOCKHART CLARKE ON CERTAIN FUNCTIONS OF THE SPINAL 
when their connection with the grey substance was interrupted. Nothing, however, is 
more certain than that the posterior roots are in immediate connection exclusively with 
these columns, which are separated from the antero-lateral columns by the posterior 
lateral fissure, through which a few only of the roots proceed to the grey substance. 
It is difficult, therefore, to conceive how sensory impressions can be conveyed after 
destruction of the posterior columns, as appears to have taken place in cases put on 
record by several observers. The only explanation of which these cases seem to 
admit, is that either these columns were only partially destroyed, or that sensory 
fibres are contained also in the anterior roots. 
The question, then, remains, ™-By what means are impressions which are received 
bv the chord transmitted upwards to the brain? 
By VoLKMANN it is believed that all, or nearly all the fibres of the nerve-roots 
terminate in the grey substance of the chord. In support of this opinion, ^ e 
endeavours to show, both by measurement and weight, that there is no progressive 
increase, from below upwards, in the size of the white columns ; that, on the contrary, 
he found these columns absolutely smaller in the cervical region than in the lower 
parts and everywhere in direct proportion to the quantity of the grey substance. He 
furth’er states, that the total area of all the spinal nerves cut transversely is many 
limes greater than the area of a transverse section of the chord above the first 
cervical nerve. Opposed to that of Volkmann is the opinion of Kolliker^ who 
holds that the white columns of the chord are composed entirely of fibres derived 
from the spinal nerves. This opinion is founded on the fact pointed out by him,— 
and about the same time by myself,— that at least a large proportion of both roots 
after passing through various parts of the grey substance, pursue a longitudinal 
course within the white columns. He further maintains, in opposition to Volkmanx, 
that these columns do really increase progressively towards the brain, and that the 
nerve-fibres of which they mainly consist, do not recover their original diameter 
which they lost in passing through the grey substance. From these facts he calcu- 
lates that the white columns are sufficiently large m the cervical region to gne 
passage to all the spinal nerves, and that they form the channels of communication 
to and from the brain. 
The results of my own observations are opposed to those of Volkmann, and par y 
in favour of those of Kolliker. In all the Mammalia examined by myself, I have 
found the quantity of the white substance of the chord absolutely greater in the 
cervical region than elsewhere. It cannot therefore be, as stated by Volkmann, m 
direct proportion to the grey substance, since the latter is far more abundant m the 
lumbar enlargement. Again, his opinion that all, or nearly all the spinal nerves 
terminate in the grey substance of the chord, is refuted by the fact, shown by ot i 
Kolliker and myself, that at least a great number of them do really pass out of t le 
grey substance as longitudinal fibres of the white columns. But on the other hand, 
* Mikroskopische Anatomie, Band ii. 
