562 NERVOUS SYSTEM 



renewed in the same place. The animal made an ineffectual effort to 

 reach the spot with the amputated member, and failing in this, after 

 some general movements of the limbs, rubbed the spot with the foot of 

 the opposite side. 



It has been thought that this experiment shows a persistence of 

 sensation and the power of voluntary movements after removal of the 

 entire encephalon ; but it must be remembered that the cord contains 

 cells collected probably into groups that correspond to sets of muscles 

 concerned in coordinate movements, and that many movements set in 

 action by an effort of the will continue in an automatic manner, as the 

 ordinary movements of progression. It is more reasonable to suppose 

 that a persistent stimulation of the surface, such as is produced by the 

 action of acetic acid on the skin of a frog, can give rise to coordinate 

 movements of a purely reflex character than to assume that the move- 

 ments in Pfliiger's experiment were voluntary efforts to remove a painful 

 impression. It is certain that in the higher classes of animals after re- 

 moval of the encephalon, in experiments on decapitated criminals and 

 in patients suffering from paraplegia, there is no evidence of centres 

 of true sensation or volition in the spinal cord. In man and the higher 

 animals, all muscular movements that depend solely on the reflex action 

 of the cord must be regarded as automatic and independent of con- 

 sciousness and volition. 



Some of the confusion in regard to the precise nervous mechanism 

 of many movements executed by the adult man may be removed by 

 an exact comprehension of the terms used in their description. There 

 are certain movements that are entirely independent of sensation and 

 volition and of practice and education. Such are the movements of 

 the lower extremities in paraplegia, movements of the stomach and 

 intestines and the movements of tranquil respiration. These may be 

 called purely reflex, depending entirely on the action of the cord or the 

 bulb. So-called purposive movements may be included in this category, 

 at least when they occur in such instances as that of the brainless frog 

 that swims or jumps. The nerve-impulses there may be assumed to be 

 conducted along constant and habitual paths in the cord. Another 

 class of movements, that has its highest illustration in man, embraces 

 those that are habitual or highly skilled. These may be called auto- 

 matic. They may be initiated by an effort of the will but continue 

 without further thought or attention. Such movements are those 

 of walking, skating, swimming, in certain instances playing on musical 

 instruments and. doing mechanical work. It seems more reasonable to 

 regard such movements as due to the action of the spinal cord than to 

 invoke what has been called "unconscious cerebration"; for while these 



