NERVE-CENTRES IN THE SPINAL CORD. 597 



and disease of the cells of the posterior gray matter of the cord. As the 

 cells are affected, there follows ascending secondary degeneration of the col- 

 umns of Goll. It is fair to assume that the disease of the cells of the gray 

 matter of the cord and of the posterior roots of the spinal nerves is con- 

 nected with the disorders of general sensibility. The disease of the columns 

 of Burdach produces the disorder in movements. 



Reasoning from the characteristic phenomena and the essential patholog- 

 ical conditions of the cord in typical cases of locomotor ataxia, the posterior 

 white columns of the cord, connecting cells of the gray matter in different 

 planes with each other, assist in regulating and co-ordinating the voluntary 

 movements. The fibres of these columns also connect the cord with the 

 cerebellum, which has an important office in muscular co-ordination. It is 

 probable that the appreciation of the muscular sense and the sense of press- 

 ure, if these can be separated from what is known as general sensibility, 

 are connected with the action of the fibres of the posterior white columns. 



NERVE-CENTRES IN THE SPINAL CORD. 



It has long been known that decapitation of animals does not arrest mus- 

 cular action ; and the movements observed after this mutilation present a 

 certain degree of regularity and have been shown to be in accordance with 

 well defined laws. Under these conditions, the regulation of such move- 

 ments is effected through the spinal cord and the spinal nerves. If an ani- 

 mal be decapitated, leaving only the cord and its nerves, there is no sensa- 

 tion, f 01 the parts capable of appreciating sensation are absent ; nor are 

 there any true voluntary movements, as the organ of the will is destroyed. 

 Still, in decapitated animals, the sensory nerves are for a time capable of 

 conducting impressions, and the motor nerves can transmit a stimulus to the 

 muscles ; but the only part capable of receiving an impression or of generat- 

 ing a motor impulse is the gray matter of the cord. If in addition to the 

 removal of all of the encephalic ganglia, the cord itself be destroyed, all mus- 

 cular movements are abolished, except as they may be produced by direct 

 stimulation of the muscular tissue or of individual motor nerves. 



The gray matter of the brain and spinal cord is a connected chain of 

 ganglia, capable of receiving impressions through the sensory nerves and of 

 generating motor impulses. The cerebro- spinal axis, taken as a whole, has 

 this general office ; but some parts have separate and distinct properties and 

 can act independently of the others. The cord, acting as a conductor, con- 

 nects the brain with the parts to which the spinal nerves are distributed. If 

 the cord be separated from the brain in a living animal, it may act as a cen- 

 tre, independently of the brain but the encephalon has no communication 

 with the parts supplied with nerves from the cord, and it can act only upon 

 the parts which receive nerves from the brain itself. 



When the cord is separated from the encephalon, an impression made 

 upon the general sensory nerves is conveyed to its gray substance, and this 

 gives rise to a stimulus, which is transmitted to the voluntary muscles, pro- 

 ducing certain movements, independently of sensation and volition. This 



