TENDON JERKS; SENSORY PATHWAYS IN SPINAL CORD 831 



classes: protopathic, epicritic, and deep or muscular. It is important 

 now for us to consider what becomes of each of these impulses after 

 entering the spinal cord, for there is abundant evidence that they travel 

 up to the brain by different pathways. This evidence is furnished partly 

 by examination of the cord of patients who during life exhibited per- 

 versions of the skin sensations, and partly by producing experimental 

 lesions affecting different parts of the spinal cord in animals. In the 

 disease syringomyelia, for example, enlargement of the central canal 

 of the spinal cord causes rupture of certain of the tracts and a conse- 

 quent disintegration of the skin sensations; that is, the sensations of pain 

 and temperature disappear, whereas those of touch and deep muscular 

 sensation remain. Or, from the experimental side, if we make a lateral 

 hemisection of the spinal cord, then after recovery, so far as we can 

 study it in a dumb animal, we shall be able to show that certain sen- 

 sations have disappeared, whereas others remain. It is evident, how- 

 ever, that we must judge by objective and not by subjective phenomena 

 in these experiments, and our results are only approximate and very 

 liable to misinterpretation. Important contributions to this subject have 

 recentty been made, particularly by Holmes 5 and by Collier, 9 on sol- 

 diers wounded in the spinal cord. 



Summing up the results obtained by the earlier investigators, Brown- 

 Sequard some sixty years ago stated that hemisection of the cord on one 

 side produced the following results: (1) paralysis of voluntary motion 

 of the same side; (2) paralysis of vasomotor control on the same side, 

 so that the limb is hotter than normal; (3) anesthesia for all kinds of sen- 

 sation, except muscular sense on the side opposite to that of the lesion; 

 (4) a condition of heightened skin sensitivity (called hyper esthesia) on 

 the same side as the lesion, with the exception of a narrow strip of skin 

 corresponding to the segment at which the cord is cut, which is anesthetic. 

 These results indicate that in general the skin sensations of pain, touch, 

 and temperature cross over to the other side shortly after their entry 

 into the cord, but that the deep muscular sensations remain in large 

 part uncrossed. More recent experimental and clinical investigations 

 do not support Brown-Sequard's conclusions. 



Ransom has recently shown that the afferent roots of the spinal cord 

 contain both medullated and nonmedullated nerve fibers, and he be- 

 lieves that the former transmit the epicritic sensations, and the latter 

 the protopathic. By tracing those different kinds of fibers into the 

 spinal cord, he found that the nonmedullated lie in Lissauer's tract for 

 one or two segments and then pass into the substantia gelatinosa Bo- 

 landi, which, therefore, appears to be the nucleus for the reception of 

 the protopathic impulses. 



