14 REFLEX ACTION 



excited to the performance of peristaltic movements and 

 other functions. 



Similarly a brainless crayfish will seize a bit of food in 

 its small chela, pass it forward to the maxillipeds, which 

 cooperate to bring it between the mandibles where it is 

 chewed, after which it is swallowed, passing into the 

 stomach, where it sets in action the gastric mill resulting 

 in the further trituration of the food. 



Reflex actions may be inhibited in various ways. If the 

 spinal cord of a frog is severed, and a stimulus applied to the 

 anterior cut end at the same time the hind toe is pinched, 

 the withdrawal of the leg which occurs regularly under nor- 

 mal conditions may be prevented from taking place. Im- 

 pulses passing down the cord block or inhibit impulses tend- 

 ing to pass down the motor nerves to the leg. Strong stimuli 

 applied to the optic lobes or certain other parts of the brain 

 of a frog produce the same effect. Reflex acts in animals 

 generally take place more readily and more uniformly if the 

 brain be destroyed, indicating that the brain acts as a con- 

 stant inhibitory organ upon the lower nerve centers. Stim- 

 uli applied to other parts of the body may also inhibit 

 reflexes. If one toe of a decapitated frog is strongly stimu- 

 lated by being held in dilute sulphuric acid and the other 

 toe stimulated by an electric current, the withdrawal of the 

 latter will be delayed or entirely checked. 



To designate as reflex action the direct responses of the 

 lowest animals which are devoid of a nervous system is to ex- 

 tend somewhat the original meaning of the term. These re- 

 sponses, however, are now commonly spoken of as "reflexes" 

 and they are very similar to the simple reflex acts of higher 

 forms in which a nervous arc forms the pathway of the 

 impulses. To a certain extent all living matter conducts 

 etimuli and hence performs the function of nervous tissue. 



