REFLEX ACTION OF THE SPINAL COED. 



599 



nected Avith reflex action are probably in the anterior fundamental fasciculi, 

 the anterior radicular zones and the mixed lateral columns. 



It is well known that the reflex excitability of the cord is exaggerated by 

 removal of the encephalon. According to Setschenow (1863), certain parts 

 in the encephalon, particularly the optic lobes in frogs, exert an inhibitory 

 influence over the reflex acts of the cord, and as a consequence, the reflex 

 phenomena are more marked when this influence is suppressed. 



Various poisons, especially strychnine, have a remarkable influence over 

 reflex excitability. In a frog decapitated and poisoned with strychnine, no 

 reflex movements occur unless an impression be made on 

 the sensory nerves ; but the slightest irritation, such as a 

 breath of air, throws the entire muscular system into a 

 condition of violent tetanic spasm. The same phenome- 

 na are observed in cases of poisoning by strychnine or 

 of tetanus in the human subject. 



The inhalation of anaesthetic agents may abolish all 

 of the ordinary reflex phenomena. Whether this be due 

 to an action upon the cord itself or to a paralysis of the 

 sensory nerves, it is difficult to determine. Ordinarily, 

 in animals rendered insensible by anaesthetics, the move- 

 ments of respiration continue ; but these also may be 

 arrested, as has been observed by all who have experi- 

 mented with anaesthetics, especially with chloroform. A 

 common way of determining that an animal is complete- 

 ly under the influence of an anaesthetic is by noting an 

 absence of the reflex act of closing the eyelids when the 

 cornea is touched. 



It is only necessary, after what has gone before, to in- 

 dicate in a general way certain phenomena observed in 

 the human subject which illustrate the reflex action of 

 the cord. It is a common observation, in cases of para- 

 plegia in which the lower portion of the cord is intact, 

 that movements of the limbs follow titillation of the soles 

 of the feet, these movements taking place independently 

 of the consciousness or the will of the subject experi- 



, , . , , .,-. , FIG. 218. Frog poisoned 



mented upon. Acephalous foetuses will present general with strychnine (Li6- 

 reflex movements and movements of respiration, and will 

 even suck when the finger is introduced into the mouth. Observations of 

 this kind are so familiar that they need not be cited in detail. Experiments 

 have also been made upon criminals after decapitation ; arid although the re- 

 flex phenomena are not so well marked and can not be excited so long after 

 death as in cold-blooded animals, they are sufficiently distinct. 



General muscular spasms following stimulation of sensory nerves are 

 pathological and take place only when the reflex excitability of the cord is 

 much exaggerated. Examples of this action are the spasms observed in teta- 

 nus or in poisoning by strychnine. In experiments on the lower animals, 



