FUNCTIONS OF THE SPINAL CORD. 631 



seem to decussate nearly in the same plane as that at which they enter the 

 cord. 1 It would appear that the smallest longitudinal column or transverse 

 layer of the gray substance remaining intact, may serve to a certain limited 

 extent as a means for the conduction of the sensory impressions of either 

 side. The central portions of the gray substance are the most effective in 

 the transmission of sensations, much more so at all events than either the 

 anterior or posterior cornua (Brown-Sequard). 



501. M. Browu-Sequard has adduced 2 very strong evidence in favor of 

 there being special conductors in the spinal cord for the sensations of touch, 

 pain, tickling, and temperature, besides those conveying motor impulses, 

 none of which can convey other sensations than their own, and he considers 

 that clinical facts demonstrate that each of these four species of sensory 

 nerves occupies a distinct part of the cord, those coming from the inferior 

 extremities, and a great part of the trunk forming a group which in the 

 upper part of the cervical region is placed behind those proceeding from the 

 thoracic members, all of which decussate in the spinal cord. Dittmar 3 even 

 goes beyond this, and contends that there are special fibres which respond 

 only to mechanical, chemical, and electrical stimuli respectively. They 

 exert, he thinks, a reflex action through the vaso-motor centre upon the 

 vessels, producing increase of blood-pressure. M. Browu-Sequard 4 has also 

 satisfied himself by experiment that the nerve-fibres employed in making 

 muscles contract in fits of epilepsy are quite distinct from voluntary motor 

 nerve-fibres, and that whilst the voluntary motor nerve-fibres are chiefly in 

 the anterior gray and white parts of the cord, the others are chiefly in the 

 lateral column, and this is in accordance with the observation of M. Charcot, 

 that inflammation (sclerosis) of the lateral column of the spinal cord is in- 

 variably accompanied by strong muscular spasms. The conductors minister- 

 ing to the muscular sense, on the other hand, like those which convey the 

 mandates of the will to the muscles and the vaso-motor nerve, do not decus- 

 sate in the cord. The conductors for impressions of temperature in the 

 dorsal region of the cord and in the cervical enlargement appear to occupy 

 the central parts of the gray substance; the conductors of impressions of 

 pain are more disseminated, and are found in the lateral and posterior parts 

 of the gray substance, whilst the conductors of the impressions of touch and 

 tickling are chiefly situated in the anterior parts of the gray substance. A 

 very remarkable result of section of one-half of the Spinal Cord is that, 

 besides the anaesthesia which is established on the opposite side of the body, 

 there is produced a state of exalted sensibility or hypenesthesia on the same 

 side. 5 This condition, made apparent by the cries of the animal on the 

 slightest pricking or pinching of the skin, begins to appear a few hours 

 after the operation, rapidly attains its full intensity, and continues to be 

 well marked for from 17 to 22 days in dogs, and from 12 to 16 days in 

 cats ; after which, according to Schiff, 6 it gradually decreases, until at length 

 the sensibility falls below its normal acuteuess. M. Brown-Sequard has, how- 

 ever, observed it to persist in guinea-pigs, though not in a very high degree 

 of intensity, for many months after the operation. The cause of this phe- 

 nomenon has not been accurately determined. It is certainly accompanied 

 by an increased flow of blood and increased temperature of the parts to 

 which the nerves are distributed,. and hence may be due to paralysis of the 



1 See Masius and Vanlair, Centralblatt, 1870, p. 1. 



2 Soe his Journal de Physiologic, 1863-1865; Archives de Physiologic, 1868. 



3 Ber. d S;ichs. Gesell. d Wiss., 1870, p. 18. 



4 Lancet, 1870, vol. i, p 2. 



6 See Brown-Sequard, Central Nervous System, 1860, p. 19. 6 Op cit., p. 275. 



