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 
codperate 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 totheleg. 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 are forms the pathway of the 
impulses. To a certain extent all living matter conducts 
stimuli and hence performs the function of nervous tissue. 
