270 SPECIAL PHYSIOLOGY. 



the multipolar ganglionic cells. Hence, these fibres serve, some, as 

 fibres of connection with the gray matter of both sides of the cord ; 

 some, to associate different nerves of the same, or of opposite sides ; 

 and possibly others, to connect the nerves directly with the gray ner- 

 vous centres at the base of the encephalon. Besides this, there prob- 

 ably exist transverse, and perhaps longitudinal, commissural fibres 

 proper to the cord itself. 



Physiological experiments, especially those made by Brown-Se'quard, 

 by dividing some portions of the cord, and leaving others, show that 

 the effects of sensory impressions pass through the white substance 

 for a certain distance upwards and downwards, into the gray matter, 

 and then cross over to the gray matter of the opposite side of the cord, 

 and so ascend towards the brain. This conducting power is said to be 

 greater in the central part of the gray matter, than in the cornua. 

 The path of sensations appears to be chiefly in the gray matter of the 

 central parts, and of the posterior half of the opposite side of the cord. 

 The white posterior columns do not appear, in any way, to assist in 

 conveying the effects of sensory impressions upwards. The experi- 

 ments from which these conclusions are drawn, consist, first, in di- 

 viding or destroying the posterior white column with the point of its 

 cornu of gray matter, in which case sensation is retained in the parts 

 below the injury; and, secondly, in preserving the posterior column 

 and gray cornu, and dividing or crushing all the rest, when sensation 

 is lost. To show the divergence of the paths of sensation, upwards and 

 downwards, the ascending and descending posterior roots of the nerves 

 are traced far into the gray matter, which is then cut, first above, and 

 then below the nerves: it is found that sensation is not completely de- 

 stroyed, till the gray matter is cut in both directions. So, also, when 

 the posterior columns are divided transversely, both surfaces continue 

 to conduct sensory impressions, showing the descent of these impres- 

 sions in the lower part of the cut cord, before they cross over to the 

 opposite side. In proof of the decussation of the path of sensations, 

 it is found that, on dividing the right half of the cord, in the neck or 

 back, sensibility ceases on the opposite side of the body only, whilst 

 motion is destroyed only on the same side. An additional remarkable 

 result takes place viz., that, on the same side as the cut, especially 

 when this is in the posterior portion of the cord, the sensibility is, 

 after a few hours, much exalted, and remains so for many days, or, 

 to a slight degree, for months. This effect, it is conjectured, is due to 

 a dilatation of the minute vessels of the parts on that side, through 

 the suspension of the action of certain sympathetic vasi-motor nerves, 

 which are connected with the injured part of the cord. This increase 

 of sensibility, or hypercesthesia, is accompanied by fulness of the ves- 

 sels, and by an elevation of the temperature of the part. It may be 

 due to simple inflammation, propagated from the wounds inflicted on 

 the cord, and on the soft parts and bones, in exposing the cord itself. 

 It has been seen after section of the anterior or motor columns alone. 

 It has also been stated, by able experimenters, that in dividing the 

 cord on one side, there is a certain diminution of sensation on both 

 sides, but a greater one on the opposite side ; any remaining appear- 



