SPINAL CORD AND COMMENCEMENT OF MEDULLA OBLONGATA. 175 



part of the fibres of the posterior roots which run in these columns stand in some 

 sort of relation to this sense. The motor power is not diminished by disease of 

 the posterior columns. 



If the gray matter of the anterior horns is injured by a pathological process, 

 there appears paralysis of the related muscles, just as in case of injury to the 

 peripheral nerves. These paralyses are followed with unusual rapidity by atrophy 

 of the affected muscles. This affection resembles the peripheral paralyses, also, 

 in the fact that the paralyzed muscles react to the electric current as though 

 their nerve-supply had been cut off. We think, from these facts, that we are 

 justified in assuming that trophic centres for the muscles and nerves are situated 

 in the anterior horn. The section experiment proves this. No matter where the 

 anterior root is severed, be it far from or near to the spinal cord, its nerve always 

 degenerates toward the periphery ; while the posterior root, divided in like 

 manner from the cord, remains in a great measure normal as long as its union 

 with the spinal ganglion remains undisturbed. 



If the fibres of the anterior roots are divided in the lateral columns between 

 their cells in the anterior horn and the brain, there generally results only paralysis 

 and no atrophy. From the accompanying diagram (Fig. 103), which shows the 

 connection between the central and peripheral portions of a motor tract, you will 

 easily understand the reason of this phenomenon. 



A disease situated in the line xac, or, rather, in the fibres represented by the 

 line, leads to paralysis. If it interrupts the conductivity of the fibres above the 

 ganglion-cells (at a or x), it has the character of a central paralysis without 

 atrophy, and often results in an improvement, or even a cure, probably because 

 other tracts act vicariously for it. If, however, the tract xa c is interrupted in the 

 ganglion-cell, or at any part of c, then not only paralysis occurs, but the paralyzed 

 fibres disappear, and the muscles supplied by them become atrophied. In this 

 case there is little prospect of a cure. Occasionally, after long-protracted disease 

 of the part x a, the part c is finally involved. This, however, is rare. A break 

 in the tract at a leads to a descending degeneration from the point of injury to the 

 corresponding anterior horn. The trophic centres for this part of the motor tract 

 must, therefore, be sought for centrally from the point of interruption, probably 

 in the cortex. As an example of paralysis and atrophy following disease of the 

 anterior horn, I will cite infantile spinal paralysis. In this disease there occurs a 

 sudden complete paralysis of distinct groups of muscles, soon followed by atrophy 

 of the muscles themselves. An examination of the spinal cord reveals disease-foci 

 affecting the gray matter of the anterior horns. The nerves, too, and even the 

 anterior roots, gradually become atrophic. The spinal cord and the roots present 

 somewhat the appearance shown in Fig. 105 A and B. 



We are not yet in possession of a sufficient number of accurate and pains- 

 taking observations to enable us to say what symptoms will result from a disease 

 of the gray matter of the posterior horns A comparison, however, of the cases 

 of tabes dorsalis in which it was affected, and of those in which it was not, 

 make it probable that a disease affecting this region would give rise to sensory, 

 and especially to trophic, disturbances of the skin. In the vicinity of the basal 

 portion of both anterior and posterior horns there must be situated tracts or 

 centres, which stand in some relation to the trophic innervation of the skin and 

 its blood-vessels. We must also look in this region for the mechanism which 

 underlies the temperature-sense. 



