THE SYMPATHETIC SYSTEM 401 



system is smaller than the central system, but is very 

 important. It has for its special work the control of the 

 internal organs, such as the stomach, liver, etc. It also 

 controls the skin, with its blood vessels and sweat glands. 

 In addition, it has charge of other parts of the body that 

 are not reached directly by the brain and the spinal cord. 



The sympathetic system gets its name from the fact that by con- 

 necting the different internal organs it sees to it that they act "in 

 sympathy with" one another. 



While the ganglia of the sympathetic system are found in many 

 parts of the body, they are most abundant in two chains that are placed 

 in front of the spinal column, one on each side of it. The plexuses are 

 very complex ganglia of the sympathetic system. The solar plexus is 

 one of these; it has been called the "brain of the abdomen." It is 

 behind the "pit of the stomach," and is so important for all the com- 

 mon body functions that there is danger of instant death if it is injured. 

 For this reason a blow in the region of the stomach is very serious. 



The sympathetic system is not independent of the 

 central system, but is a part of it. This is illustrated by 

 a simple case. When food gives a stimulus to the afferent 

 nerve fibers of the stomach, they carry the message to 

 certain sympathetic ganglia. The ganglia cannot turn 

 the message back to the gastric glands, directing them to 

 secrete the gastric juice; the ganglia must send the 

 message on to the central system. Then, if the demand 

 is a normal one, such as the call for gastric juice, the lower 

 parts of the central system (the spinal cord or the bulb, 

 for example) can send the efferent, or motor, impulses. 

 The return message goes through efferent axons and the 

 sympathetic ganglia to the secreting glands. In such a 

 case the upper brain (cerebrum) has no part in the 



