448 STUDIES IN ADVANCED PHYSIOLOGY. 



fingers the sensation produced by the burning is carried to 

 the reflex centers in the spinal cord and by these reflex 

 centers motor impulses are sent out to remove the hand. 

 These motor impulses are in harmony with the incoming 

 impulses and are intended for specific purposes. 



The medulla oblongata contains many of the higher re- 

 flex centers. Such, for instance, as the reflex centers oc- 

 casioning respiration; the reflex center controlling the 

 general vascular supply ; the reflex center regulating the 

 general temperature of the body, and others. In the brain 

 are reflex centers co-ordinating sensations and motions 

 without the intervention of consciousness, while in the 

 spinal cord are quite a number of centers concerned in the 

 manipulation of the trunk and limbs. 



3. Junction Centers. In addition to the automatic cen- 

 ters which seem to have the power to originate nervous 

 impulses and the reflex centers which are able to co-ordi- 

 nate sensations and movements without appealing to con- 

 sciousness there are a number of ganglia, the function of 

 which seems to be entirely that of a relay station or junction 

 center. For instance, the spinal root ganglion is in all prob- 

 ability nothing more than a relay station serving merely to 

 act as a center of nourishment and strength to the nerve 

 fiber itself, and having nothing to do with the impulses 

 traversing it save to make more possible their transmission. 

 Much as in a system of telegraph wires there are relays of 

 batteries, from time to time, concerned only in making the 

 transmission of the impulses originated in other ways pos- 

 sible. In still other cases nerve centers seem to be mere 

 junction centers; that is, centers of distribution. A single 

 impulse running into such a center will be distributed 

 through the many cells in that center and flow out of it in- 

 creased many fold. The ganglia in the mesentery and ali- 

 mentary canal probably serve in this manner and make 

 possible that the few impulses reaching these organs will be 

 finally multiplied and distributed as to reach each individual 

 muscle fiber composing them. 



