SPINAL COED AND NEEVES 311 



the abolition of sensation and volition takes place gradually, and 

 is not complete till the narcosis has been carried so far as to 

 inhibit the movements that we consider " reflex " because they 

 are excited by external stimuli. 



The second method is founded on the assumption that the 

 psychical functions are localised exclusively in the brain. But 

 this, as we shall see, is far from certain. It is doubtful whether 

 the spinal cord severed from the cerebrum may not also be capable 

 of function as an organ of sensation, albeit an imperfect one, and 

 whether the excitation of its afferent nerves may not avail to 

 excite traces of consciousness and motor impulses, since there is a 

 choice of efferent paths by which the excitation can be transmitted 

 to the peripheral motor organs. 



Hence it is not possible in studying the functions of the spinal 

 cord to make a sharp distinction between purely reflex and 

 voluntary acts, since there is no objective sign by which a clean 

 line of separation can be drawn between them. The purposive, or, 

 as Goltz calls it, the responsive, character, or property of carrying 

 out movements directed to a given end, is common to both reflexes 

 and voluntary actions, as appears from the experiments made on 

 cold- as well as on warm-blooded animals. 



We are therefore constrained to make an objective study of 

 the characteristics and manifestations of the reflex acts which the 

 spinal cord is able to carry out independently of the brain. 



Whytt (1750) was the first who demonstrated that the agency 

 of a central organ is necessary for the transmission of excitations 

 from afferent to efferent nerves. As soon as the grey matter of 

 the cord is destroyed every reflex movement ceases. The same 

 author showed that reflex action does not depend on the integrity 

 of the cord as a whole, but that an isolated segment suffices for the 

 reaction. If in the decapitated frog the cord is divided at the 

 level of the fifth spinal nerves, reflexes in both the fore- and the 

 hind-limbs are obtained on exciting the skin. The reflex centre 

 for the former is located in the ventral enlargement, for the 

 latter in the dorsal enlargement of the cord. A striking 

 example of a vigorous and sustained reflex in the frog, first 

 noticed by Spallanzani, is the sexual clasp, which persists after 

 dividing the cord above and below the two large nerves of the 

 brachial region (second and third cervical pairs). The lizard's tail, 

 like that of the eel, can be divided into a number of pieces, each 

 of which preserves reflex activity for some time. The lumbo- 

 sacral region of the cord can be longitudinally split up into two 

 halves, each of which is capable of reflex movements so long as 

 the grey matter is left intact. The functional capacity of isolated 

 parts of the spinal cord is the physiological evidence of its 

 metamerism. In the higher warm-blooded animals the function 

 of the segments is obscured by the phenomena of shock, which 



