REFLEX FUNCTION OF THE SPINAL CORD 501 



when the influence of the mind is completely removed ; as 

 when food is introduced into the fauces or pharynx during 

 a state of complete coma, or in a brainless animal. 



So also, for example, under the influence of the spinal 

 cord, the involuntary and unfelt muscular contraction of 

 the sphincter ani is maintained when the mind is com- 

 pletely inactive, as in deep sleep, but ceases when the 

 lower part of the cord is destroyed, and cannot be main- 

 tained by the will. 



The independence of the mind manifested by the reflect- 

 ing power of the cord, is further shown in the perfect 

 occurrence of the reflex movements when the spinal cord 

 and the brain are disconnected, as in decapitated animals, 

 and in cases of injuries or diseases so affecting the spinal 

 cord as to divide or disorganize its whole thickness at any 

 part whose perfection is not essential to life. Thus, when 

 the head of a lizard is cut off, the trunk remains .standing 

 on the feet, and the body writhes when the skin is irritated. 

 If the animal be cut in two, the lower portion can be ex- 

 cited to motion as well as the upper portion : the tail may 

 be divided into several segments, and each segment, in 

 which any portion of spinal cord is contained, contracts on 

 the slightest touch ; even the extremity of the tail moves 

 as before, as soon as it is touched. All the portions of the 

 animal in which these movements can be excited, contain 

 some part of the spinal cord ; and it is evidently the cause 

 of the motions excited by touching the surface ; for they 

 cannot be excited in parts of the animal, however large, if 

 no part of the cord is contained in them. Mechanical irri- 

 tation of the skin excites not the slightest motion in the 

 leg when it is separated from the body ; yet the extremity 

 of the tail moves as soon as it is touched. The same power 

 of the spinal cord in reflecting impressions will cause an 

 eel, or a frog, or any other cold-blooded animal, to move 

 along after it is deprived of its head, and when, however 

 much the movements may indicate purpose, it is not 



