TONIC ACTIVITY OF THE CORD 201 



cross mainly in the sensory decussation of the medulla. There 

 exists a great deal of uncertainty as to the exact paths followed 

 by the different cutaneous sensations. In syringomyelia, a 

 condition in which cavities are formed in the gray matter, a 

 frequent symptom is the loss in certain regions of sensibility 

 to pain and to changes of temperature, while tactile sensibility 

 is unaffected. In locomotor ataxia, in which there is an inco- 

 ordination of movement, a degeneration in the posterior columns 

 of the cord is an almost constant lesion. Afferent impulses 

 from muscles and tendons resulting in tactile sensations and 

 others serving as the basis of muscular sense, pass along these 

 columns. The tracts of Gowers and Flechsig also probably 

 carry impulses from muscles and tendons. The short endo- 

 genous fibers of the anterolateral column constitute a path 

 in man for pain and temperature impressions a path which 

 is mainly or entirely a crossed one. The posterior columns 

 have nothing to do with the conduction of painful impressions. 

 Division of them causes hyperesthesia rather than anesthesia. 

 If left intact, while the rest of the cord is cut, the animal is 

 insensitive to pain below the level of the lesion. 



Effects of Removal of the Spinal Cord. It is necessary to per- 

 form this operation in several successive steps. The cord is 

 first sectioned in the upper thoracic region, and then at suc- 

 cessive times the lower thoracic, lumbar, and sacral region 

 are removed. Very great care is required in the treatment of 

 animals, but some have lived for long periods, during which the 

 digestive, circulatory, and excretory organs performed their 

 functions normally. The muscles of the hind limbs and trunk 

 underwent complete atrophy. The bloodvessels, paralyzed at 

 first, gradually recovered their tone. Taken all together, the 

 animal showed a decided lack of adaptability. Its power of 

 preserving a constant temperature was more limited than 

 normal, and the susceptibility to inflammatory disturbances 

 in the visceral organs was greatly increased. 



Tonic Activity of the Cord. In performing Brondgeest's 

 experiment, a frog whose brain has been destroyed is sus- 

 pended so that the legs hang down. Then one sciatic nerve is 

 cut. As a result the leg on the corresponding side hangs a 

 little straighter than the other. This is due to the fact that 

 the feeble impulses which the cord is continually discharging 



