736 IRRITABILITY OF THE SPINAL CORD. 



included with the coordinated reflexes of the musculature of the trunk and the 

 extremities. 



Muscular Tone. Automatic functions also were formerly credited to the spinal 

 cord, one of which was a certain moderate degree of active tension of the muscles 

 that is designated tone. It was thought that the tone of the transversely striated 

 fibers was demonstrated by the retraction of the extremities of a divided muscle, 

 but this is due simply to the circumstance that all of the muscles are somewhat 

 stretched beyond their normal length, and for this reason also paralyzed muscles, 

 which must have lost their nervous tone, exhibit exactly the same phenomenon. 

 Also the increased contraction of certain muscles after paralysis of their antagonists, 

 and the distortion of the face toward the healthy side after unilateral facial paraly- 

 sis, have been cited as examples of tone. These, however, are due to the fact that 

 after activity of the intact muscle strength is wanting to restore the parts affected 

 to the normal median position of rest. The following experiment of Auerbach 

 and Heidenhain is opposed to the assumption of a tonic contraction. If the 

 muscles of a decapitated frog's leg be made tense, they do not elongate after 

 division of the sciatic nerve, or after paralysis of jthis nerve by application of 

 ammonia or carbolic acid. If, however, a decapitated frog is suspended in an 

 abnormal position, it will be observed that if the sciatic nerve on one side or the 

 posterior roots of the nerves of this extremity have been divided, then the member 

 upon this side hangs in a relaxed manner, while the member upon the intact 

 side is slightly retracted. The sensory nerves of the latter are by the weight of 

 the member thrown permanently into a state of gentle stimulation, so that by 

 this means a slight reflex retraction upward of the member is brought about, 

 which fails to occur as soon as the sensory nerve-fibers of the member are paralyzed. 

 If the slight retraction mentioned is to be considered as tone, then it is to be 

 characterized as reflex tone. With this experiment that of Harless, C. Ludwig 

 and Cyon should be compared (p. 716). 



IRRITABILITY OF THE SPINAL CORD. 



At the present time there is no unanimity of opinion as to whether 

 the spinal cord, like a peripheral nerve, is irritable, or whether it is char- 

 acterized by the remarkable peculiarity that most of its conducting 

 paths and ganglia are without reaction to direct electrical and mechani- 

 cal stimuli. 



An outline of the views of the opposing investigators is as follows: If stimuli 

 are carefully applied to the exposed white or gray matter, neither movement nor 

 sensory perception results. In making this observation, however, the greatest 

 care must be taken to avoid irritation of the roots of the spinal nerves, as these 

 naturally react to stimuli and thus excite sensations, as well as reflex movements, 

 on the one hand, and also directly excited movements on the other hand. As 

 the spinal cord thus conveys to the brain the impulses brought to it through 

 the stimulated posterior roots, but is incapable of reacting even to stimuli exciting 

 sensory _ impressions Schiff has designated it as esthesodic, that is transmitting 

 perceptions. Moreover, as the cord is capable, in like manner, of conducting both 

 voluntary and reflex motor impulses, without, however, being itself receptive for 

 motor impulses applied directly, it is kinesodic, that is movement-conducting. 



According to Schiff, therefore, all of the results that follow stimulation of 

 the uninjured spinal cord, such as spasm and contracture, are caused by simul- 

 taneous stimulation of anterior roots, or they are reflexes from the posterior 

 columns alone or from the posterior columns and the posterior roots at the same 

 time. Diseases involving only the anterior and lateral columns never cause 

 irritative, but only paralytic symptoms. In the state of complete anesthesia and 

 in that of apnea, all stimulation is without effect. According to Schiff' s view all 

 of the centers, both spinal and cerebral, cannot be stimulated by artificial means. 

 The situation of a center can for this reason be determined onlv bv the paralvtic 

 method. 



Schiff concludes, therefore, that in the posterior columns the sensory 

 root -fibers produce pain on stimulation, but not the actual paths for the 

 posterior columns themselves. Schiff, however, observed as a sign that 

 stimulation of the actual paths caused tactile sensations, dilatation of 



