SPINAL CORD AS A CONDUCTOR. 615 



out their union with the cells being obvious or immediate. The 

 fibres of anterior roots traverse the superficial white part of the 

 cord on their way to reach the anterior gray columns, into the 

 cells of which they can be directly traced. The numerous pro- 

 cesses from these cells then pass into the fibrillar network which 

 lies between the cells and makes up the great mass of the gray 

 substance. By means of two sets of fibres (one lying in the lat- 

 eral white column on the same side, and another, which crosses 

 at once to the other side of the cord) these cells are kept in com- 

 munication with the parts of the cord above. The medullated 

 nerve fibres of the cord, then, are not directly continuous with 

 those of the roots of the spinal nerves, but seem only to have the 

 function of connecting the different regions or districts of the 

 cord with one another and with the brain, and they thus establish 

 a near relation between the cells in the lumbar, dorsal and cervical 

 regions of the spinal cord with the medulla oblongata, etc. 



Histology thus leads us to expect that the essential parts of 

 the cord are (1) innumerable fibrils in the gray matter, and 

 (2) series of groups of cells all intimately connected with one 

 another, with the cells in the masses of gray matter at the base 

 of the brain (cerebellum), and with the fibres in the anterior 

 and posterior spinal roots, by which they are related to sporadic 

 ganglia and the various tissues and organs. The white fibres of 

 the cord are then, probably, only used for the more rapid con- 

 veyance of impulses from one group of cells to some others lying 

 in a distant region of the cord itself, while the main conducting 

 work is accomplished by the fibrils of the gray matter. 



Experiments have taught us the following facts: 1. Section of 

 the cord causes loss of both sensation and motion in the part 

 behind speaking of a lower animal the point of section (Galen). 

 2. Section of one side of the cord is followed by loss of sensation 

 on the side opposite to the injury, with increased sensitiveness and 

 loss of motion (recovering slowly) on the same side. 3. Division 

 of the cord in the median line gives rise to impairment of feeling 

 in a badly-defined part of the surface, but no loss of motion. 

 4. Section of the posterior white columns gives rise to the loss 

 of perception of tactile, temperature and muscle sense, but the 



