REFLEX ACTION. 255 



of the spinal cord. One of the first symptoms of loeomotor 

 ataxia is absence of the knee jerk, which, it will be remembered, 

 is elicited by tapping the patellar tendon after putting it pas- 

 sively on the stretch, either by sitting with the feet swinging on 

 the edge of a table, or by crossing one knee over the other. Pains, 

 called crises, are also usual in various parts of the body. Later 

 symptoms are inability to stand without falling when the eyes 

 are shut, inco-ordinated walking, in which the foot is lifted too 

 high and is brought down to the ground again too violently, loss 

 of sensation of the skin of the foot and leg, and changes in the 

 pupillary reflexes of the eye (see p. 284). The joints also be- 

 come swollen and the articular surfaces roughened so that a 

 grating sensation is experienced when the joint is bent (Char- 

 cot's joint). The condition gradually gets worse, so that the 

 patient becomes bedridden. Death is usually due to complica- 

 tions. 



2. Destruction of the anterior horn cells not only causes 

 absence of reflex action, but is followed by marked atrophy of 

 the affected muscles. It has been supposed that this points to 

 a so-called trophic influence of these nerve cells, that is to say, 

 a power of influencing nutrition. Such changes occur in infan- 

 tile paralysis (poliomyelitis anterior). 



3. Stimulation of the above fibers may cause exaggeration of 

 the reflexes, as in the earlier irritative stages of neuritis, in 

 tumors pressing on the nerve roots, or when the membranes of 

 the cord become inflamed, as in meningitis. 



4. Removal of impulses coming from the cerebrum by way of 

 the pyramidal tracts causes exaggerated reflexes. Such occur 

 in paralysis of both sides of the body in paraplegia, and on one 

 side, the paralyzed, in hemiplegia. 



In a paraplegic patient the weakest stimulus applied to the 

 skin of the paralyzed portion of the body will call forth a wide- 

 spread and much exaggerated reflex contraction. 



