250 THE NERVOUS SYSTEM 



activity is limited to the area corresponding to the distribution 

 of the afferent nerve which has been irritated; but if the irrita- 

 tion be sufficiently increased other muscles in the same locality, 

 or the corresponding muscles on the opposite side of the body, or 

 even the whole musculature, may be thrown into action. This 

 is explained on the ground that under favorable conditions of 

 central excitability, strength of peripheral irritation, etc., the 

 afferent impression 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 sensory impression as 

 a simple breath of air. Removal of the encephalon in inferior 

 animals also exaggerates reflex excitability. 



5. Coordination. This has been referred to under the columns 

 of Burdach. Coordination is "a repetition of ordinary reflex 

 acts for our daily lives." No effort is necessary to coordinate 

 the muscular movements of deglutition, respiration, walking, etc. 

 These movements may be performed when the cerebrum is 

 removed. 



6. Inhibition of Reflex 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, provid- 

 ing 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 controlled. These are 

 usually performed as reflex cord acts, but the brain may evidently 

 assert its superiority over the cord and inhibit them. 



7. Special Centers. In the gray matter of the cord are found 

 various centers for distinct acts such as defecation, parturition, 

 micturition, etc. These are all connected with each other and 

 with the encephalon and obey the usual laws of reflex action. 



