738 CONDUCTING PATHS IN THE SPINAL CORD. 



The remarkable fact is worthy of mention that after unilateral division of 

 the spinal cord, or, in the rabbit, of the posterior and the innermost portion of the 

 lateral column, hyperesthesia below the level of the section appears upon the 

 same side, so that rabbits cry aloud on slight pressure being made upon the toes. 

 The phenomenon may persist for some three weeks, and it may be replaced by 

 normal or subnormal sensibility. The healthy side exhibits permanent impair- 

 ment of sensibility. Similar results have been observed in human beings with 

 like lesions. An analogous phenomenon occurs after division of the anterior 

 columns, that is, a marked tendency to contractions in the muscles below the 

 level of the section hyperkinesis. 



In the intact body the normal irritability of the spinal cord is 

 dependent upon the continuance of the normal circulation. Ligation 

 of the abdominal aorta gives rise rapidly to paralysis and anesthesia in 

 the lower portions of the body. 



Sudden total anemia, as from occlusion of the aorta, in dogs, causes at first 

 convulsions, lasting for twenty seconds; then paralysis, lasting for one minute; 

 next sensory excitation, lasting for two minutes; and finally anesthesia, lasting 

 for three minutes. Incipient degenerative processes appear in the ganglion-cells 

 in the course of a few hours. 



After prolonged ligation the anterior roots of the spinal cord and the 

 entire gray matter of the lower portion of the cord that has been rendered 

 anemic undergo degeneration. Motility and sensibility a^e permanently 

 lost in the posterior extremities. 



CONDUCTING PATHS IN THE SPINAL CORD. 



Method. The conducting paths in the spinal cord can be demonstrated by 

 means of histological examination; of no less importance is a study of the func- 

 tional disturbances exhibited by persons suffering from injury or degeneration 

 in circumscribed areas. Animal experimentation is capable of affording confirma- 

 tion in an analogous manner, although certain differences in the relations of the 

 conditions are observed as compared with those present in human beings. 



Flatau established the general law that the short paths in the spinal 

 cords are situated nearer the gray matter, and the long paths nearer 

 the surface. 



Localized tactile impressions pressure-sense, sensation of cold, muscle- 

 sense are conveyed upward through the posterior columns on the same 

 side. The conduction of the sensation of heat is said to take place 

 throughout the entire gray matter. Interruption of the posterior col- 

 umns abolishes the sense of cold, the pressure-sense, and the muscular 

 sense. The course in the brain is described on p. 745. 



The columns of Goll in the cervical cord contain continuations of the pos- 

 terior dorsolumbar and lower dorsal roots. The path for the muscle-sense is 

 through the column of Burdach; where it approaches the medulla oblongata is 

 situated the path for the muscle-sense in the arms. 



In the rabbit the path for localized tactile sensation is situated in the lateral 

 column in the lower portion of the dorsal cord. Division of certain portions of 

 the lateral column, in the rabbit, abolishes this sensation for certain related 

 cutaneous areas. Total division upon one side has the same effect for the entire 

 half of the body below the level of the section. The condition of abolished tactile 

 and muscular sense is designated anesthesia. 



The impulses for localized voluntary movements are conducted in man 

 through the anterior and lateral columns of the same side, through 

 the pyramidal tracts. At the corresponding level of the spinal cord the 

 fibers enter first into contact with the ganglion-cells of the anterior horns 

 and thence the impulses pass into the appropriate anterior root (Fig. 

 355- M). 



