REFLEX ACTION OF THE SPINAL CORD 561 



strychnin, no reflex movements occur unless an impression is made on 

 the sensory nerves ; but a slight irritation, such as a current of air, throws 

 the entire muscular system into a condition of violent tetanic spasm. The 

 same phenomena are observed in cases of poisoning with strychnin or of 

 tetanus in the human subject. 



The inhalation of anesthetic agents may abolish all the ordinary 

 reflex phenomena. Whether this be due to an action on the cord 

 itself or to a paralysis of the sensory nerves, it is difficult to determine. 

 Ordinarily, in animals rendered insensible by anesthetics, the movements 

 of respiration continue ; but these also may be arrested, as has been ob- 

 served by all who have experimented with anesthetics, especially with 

 chloroform. A common way of determining that an animal is completely 

 under the influence of an anesthetic is by noting an absence of the reflex 

 act of closing the eyelids when the cornea is touched. 



It is necessary, after what has gone before, only to indicate 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 paraplegia 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 experimented on. Acephalous monsters will present 

 general 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. Experi- 

 ments have also been made on criminals after decapitation ; and although 

 the reflex 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 exaggerated. Examples of this action are the spasms observed in 

 tetanus or in poisoning by strychnin. In experiments on the lower 

 animals, particularly frogs, coordinate reflex movements are often ob- 

 served, such as the movements of jumping or swimming. This is some- 

 times called purposive reflex action, as the movements seem to have 

 a definite purpose, or object. The following well-known experiment 

 illustrates a coordinate, or purposive reflex. 



Pfliiger removed the entire encephalon from a frog, leaving only the 

 spinal cord. He then touched the surface of the thigh over the inner 

 condyle with acetic acid. The animal thereupon rubbed the irritated 

 surface with the foot of the same side, apparently appreciating the 

 seat of the irritation, and endeavoring, by a voluntary effort, to remove 

 it. The foot of this side was then amputated, and the irritation was 



