THE HIGHER ORGANISMS 167 



plicated reflex involving the correlated action of many 

 muscles, and effected solely by stimuli conveyed to spinal 

 ganglia and impulses sent out by them. There can be no 

 doubt about the purpose of the reflex: it was to protect 

 the skin from the injurious effect of the acid. When we 

 examine the character of reflexes in general, we find them 

 purposeful, as a rule, yet destined to a purpose of which 

 the animal can be no more conscious than it is of the 

 performance of the act, which, of course, it cannot be when 

 its head is cut off or its brain destroyed. 



Thus unconsciousness of the act, at the time of its 

 commission, is a characteristic of reflex action. 



Various definitions of reflex action are given, but usu- 

 ally agree in stating that it is the unconscious and invol- 

 untary response that follows the stimulation of afferent nerve 

 fibres. Sherrington and Parmelee define reflexes as "ac- 

 tions in which there follows on an initiating reaction, an 

 end-effect reached through the mediation of a conductor 

 itself incapable either of the end-effect or, under normal 

 conditions, the inception of the reaction." According to 

 Jennings it must be an invariable response, but the in- 

 variability of the action should not be too much empha- 

 sized, as among higher animals the numerous bonds of 

 communcation between the nerve centres permit of con- 

 siderable variation. 



If two frogs, one with its telencephalon or highest brain 

 center destroyed, the other normal, be dropped into hot 

 water, each will immediately climb out if there be any- 

 thing to climb upon; but if the two frogs are placed in a 

 vessel of water which is gradually heated, the normal frog 

 will climb out when the water reaches a certain tempera- 

 ture, while the frog without a brain remains in the water 

 and cooks. To explain the behavior of the brainless frog 

 in this experiment we suppose that the sudden and violent 

 stimulation caused by the application of hot water to the 

 entire skin resulted in reflex action involving all of its 

 members in complicated and coordinated manner. When 

 the water into which the frog is placed is gradually heated, 

 however, no sudden stimulation is experienced. 



