BEFLEX FUNCTION OF THE SPINAL CORD. 507 



will is not ouly not beneficial, but positively interferes with 

 their harmonious and perfect performance. Anyone may 

 convince himself of this fact by trying to take each step as 

 a voluntary act in walking down stairs, or to form each 

 letter or word in writing by a distinct exercise of the will. 



These actions, however, will be again referred to, when 

 treating of their possible connection with the functions of 

 the so-called sensory ganglia (p. 523). 



The phenomena of spinal reflex actions in man are much 

 more striking and unmixed in cases of disease. In some of 

 these, the effect of a morbid irritation, or a morbid irri- 

 tability of the cord, is very simple ; as when the local 

 irritation of sensitive fibres, being propagated to the 

 spinal cord, excites merely local spasms, spasms, namely, 

 of those muscles, the motor fibres of which arise from, the 

 same part of the spinal cord as the sensitive fibres that are 

 irritated. Of such a case we have instances in the invol- 

 untary spasmodic contraction of muscles in the immediate 

 neighbourhood of inflamed joints ; and numerous other 

 examples of a like kind might be quoted. 



In other instances, in which we must assume that the 

 cord is morbidly more irritable, i.e., apt to issue more 

 nervous force than is proportionate to the stimulus applied 

 to it, a slight impression on a sensitive nerve produces ex- 

 tensive reflex movements. This appears to be the condition 

 in tetanus, in which a slight touch on the skin may throw 

 the whole body into convulsion. A similar state is induced 

 by the introduction of strychnia, and, in frogs, of opium, 

 into the blood ; and numerous experiments on frogs thus 

 made tetanic, have shown that the tetanus is wholly uncon- 

 nected with the brain, and depends on the state induced in 

 the spinal cord. 



It may seem to have been implied that the spinal cord, as 

 a single nervous centre, reflects alike from all parts all the 

 impressions conducted to it. But it is more probable that 



