250 THE NERVOUS SYSTEM 



send prolongations both upward and downward in the gray 

 matter. These prolongations, by their end arborizations, 

 seem to communicate indirectly with several motor cells. In 

 the simplest reflex movements connected with the spinal cord 

 the muscular activity is limited to the area corresponding 

 to the distribution of the afferent nerve which has been irri- 

 tated; but if the irritation be sufficiently increased other 

 muscles in the same locality, or the corresponding muscles 

 on the opposite side of the body, or even the whole muscu- 

 lature, may be thrown into action. This is explained on the 

 ground that under favorable conditions of central excita- 

 bility, strength of peripheral irritation, etc., the afferent im- 

 pression is disseminated by collaterals throughout a large 

 area of the cord (for example), and a large number of effer- 

 ent cells are made to discharge. The reflex excitability of 

 the cord is markedly increased by the administration of 

 such drugs as strychnin. An animal so poisoned will be 

 thrown into the most violent convulsions by so slight a sen- 

 sory impression as a simple breath of air. Removal of the 

 encephalon in inferior animals also exaggerates reflex ex- 

 citability. 



5. Coordination. This has been referred to under the 

 columns of Burdach. Coordination is "a repetition of ordi- 

 nary reflex acts for our daily lives." No effort is necessary 

 to coordinate the muscular movements of deglutition, res- 

 piration, walking, etc. These movements may be performec^ 

 when the cerebrum is removed. 



6. Inhibition of Refiex Acts. This is not a function of 

 the cord proper, but is directed by the cerebrum. A great 

 many reflex movements may be inhibited by an act of the 

 will, providing always they are due to contraction of striped 

 muscle. The reflex acts of coughing or sneezing, or those 

 resulting from tickling, for example, can be largely con- 

 trolled. These are usually performed as reflex cord acts, 

 but the brain may evidently assert its superiority over the 

 cord and inhibit them. 



