112 PHYSIOLOGY FOR NURSES 



ness called fainting by inhibiting the constrictor center 

 and allowing such dilatation of the great venous chan- 

 nels, particularly those of the abdomen, that there is too 

 little blood in the brain to maintain its normal state. 

 Nature indicates the remedy by throwing the fainting 

 person down. 



Parts of the medulla are supposed to contain various 

 other centers, such as for the control of salivary secre- 

 tion, swallowing, vomiting, etc. 



The Spinal Cord. Like other parts of the central 

 nervous system, the spinal cord consists of gray and 

 white matter, the gray being in the center and the white 

 on the outside, a converse arrangement to that of the 

 brain. While mainly employed in conducting impulses 

 to and from the brain, the cord contains many reflex 

 centers more or less under the control of the higher cen- 

 ters. 



The fissures on the front and back of the cord indi- 

 cate a partial subdivision into hemispheres, similar to 

 ihe subdivision of the cerebrum, while the large mass 

 stretching from one half to the other suggests the pres- 

 ence of commissural fibers connecting and coordinating 

 the two. The gray matter, projected in the form of ir- 

 regular horns into the front and back of each half of the 

 cord, contains the cells, the branches of which connect 

 on the one hand with the fibers of the entering nerves 

 and on the other with branches of other cells in turn con- 

 nected with the fibers of nerves leaving the cord either 

 on the same or the opposite side. Such an arrangement 

 completes the formation of a reflex arc, composed of a 

 nerve fiber connecting a sensory terminal with the re- 

 ceiving branch of the cell in the gray column, the dis- 

 patching branch of which connects with the receiving 

 branch of a cell in the motor area, the dispatching branch 



