336 INNERVATION. [CHAP. XI. 



When the polarity of the cord is greatly excited by strychnine or 

 other substances, or when tetanus exists, all parts of the surface are 

 equally capable of exciting reflex actions. The least touch will 

 cause them, not only in the limb touched, but in all that side of the 

 trunk, or even throughout the whole body. So general is the excit- 

 ation, that the least impression made on the peripheral extremity of 

 a sensitive nerve in any part of the body is instantly converted into 

 muscular spasm, more or less general. A slight current of air, in 

 tetanus, is sufficient to excite general spasm. Miiller remarks, that, 

 in such states of the' cord, the reflex actions excited by stimulating 

 the nerves themselves are much less than those produced by ex- 

 citation of the surface. 



The readiness with which a physical change, induced in one part 

 of the centre, is propagated to others, whether above or below it, is 

 due no doubt to the vesicular matter. An experiment made by 

 Van Deen illustrates this statement. If, in an animal poisoned by 

 strychnine, the cord be divided in its entire length along the median 

 line, leaving only a slight bridge of gray matter, stimuli applied to 

 any part of the surface will exhibit as extensive reactions as if the 

 cord were entire. It is evident that the only medium of commu- 

 nication between the opposite halves, must be the small portion of 

 vesicular matter left undivided. 



Impressions conveyed to the cord by the posterior roots of any 

 of its nerves, may be reflected to the corresponding motor nerves, 

 and cause movement, or may extend irregularly along the posterior 

 horns of gray matter and stimulate the nerves implanted in them, 

 and thus give rise to new sensations, which may be referred to other 

 and even distant parts of the body. 



The hypothesis, under consideration, affords us an explanation, 

 more satisfactory than any other, of the paralytic state of the sphinc- 

 ter ani in brain disease, already referred to, as well as in that of the 

 spinal cord. This muscle is certainly chiefly under the influence of 

 the will. In ordinary cases of diseased brain where the lesion is con- 

 fined to one side, the centre of volition is not sufficiently impaired to 

 affect its influence upon the sphincter. In graver lesions, however, 

 although the will may still continue to exert its control upon one 

 side of the body, it loses its power over the sphincter, which is not 

 excitable by any stimulus. In disease of the spinal cord, there i 

 paralysis of the sphincters if the lesion involve a sufficient portion 

 of the cord's substance, in whatever region of the cord it may exist 

 Even when the lesion is situate high up in the neck, or in the dorsal 

 region, leaving the lumbar portion perfectly whole, the sphincter 



