SPINAL CORD AS A CONDUCTOR. 615 



The posterior roots of the spinal nerves pass through the white 

 substance to reach the posterior gray column, where they break 

 up into numerous fine twigs, which are distributed to neighboring 

 parts of the gray network of fibrils, in which they are lost with- 

 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 func- 

 tion 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 an- 

 other, 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 gan- 

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

 cord are then, probably, only used for the more rapid conveyance 

 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 same side with increased sensitiveness and loss of motion 

 (recovering slowly) on the side opposite to the injury. 3. Divi- 



