IRRITABILITY OF THE SPINAL CORD. 737 



the pupils with each stimulation. Removal of the posterior columns 

 causes anesthesia, loss of touch. Algesia, pain-sensation, is preserved, 

 and at first there is even hyperalgesia. 



The' anterior columns cannot be stimulated so as to affect either 

 transversely striated or unstriated muscles, if only the actual tracts are 

 stimulated. Movements may occur, however, either if the motor root- 

 fibers are stimulated or if the current reaches the posterior columns, in 

 which it stimulates the sensory root -fibers and thus causes reflex move- 

 ments. 



Numerous investigators are opposed to these views and express themselves 

 in favor of the possibility of direct stimulation of the spinal cord. Pick maintains 

 that he is able to induce movements of the hind legs by irritating directly the 

 anterior columns isolated for a considerable distance in order to eliminate diffusion 

 of the current. Biedermann reaches the conclusion that the motor nerve is most 

 irritable on its transverse section. Also on transverse section of the spinal cord, 

 in the frog, feeble stimuli, such as descending opening shocks, are effective, but 

 not further downward. This observation is in favor of analogous sensibility to 

 stimuli on the part of both. According to Schiff's investigations in this con- 

 nection, however, the anterior column of the spinal cord of the frog contains, 

 in addition to the longitudinal fibers controlling movement, also sensory fibers, 

 stimulation of which may cause reflexes. Therefore, all of the observations made 

 on the anterior columns of the frogs are not available as evidence in favor of the 

 direct irritability of the motor paths in the anterior columns. The sensory fibers in 

 question are believed to rise from the gray matter and to pass within the spinal cord 

 to the anterior columns, without first making their exit through the posterior 

 roots intracentral nerves. 



The vasoconstrictors passing downward from the vasomotor center 

 through the spinal cord can be irritated within the cord by all stimuli. 

 Direct stimulation of any transverse section of the spinal cord causes 

 contraction of all of the vessels innervated below that level. In a similar 

 manner the fibers ascending in the spinal cord and exerting a pressor 

 effect upon the vasomotor center can be irritated. Their stimulation 

 causes no sensation. According to Schiff, the results obtained in these 

 observations are, however, likewise not due to direct irritation 



The spinal cord appears to be insensitive to chemical stimuli, such 

 as moistening the cut surfaces with blood. 



The motor centers can be irritated directly by blood at a temperature 

 above 40 C. and by blood from an asphyxiated person or by sudden and 

 total anemia in consequence of ligation of the aorta ; likewise by certain 

 poisons, such as picrotoxin, nicotin, barium-compounds: 



In experiments of this character the spinal cord, for example at the level of 

 the last thoracic vertebra, must have been divided some twenty hours previously, 

 in order that it shall have recovered from shock. The posterior roots in the 

 lower portion should also have been divided previously, in order to eliminate 

 any possible reflex influences. If dyspnea be induced in cats thus prepared, or 

 if their blood be overheated, extensor spasm, vascular contraction, secretion of 

 sweat, evacuation of the bladder and the rectum, as well as contraction of the 

 uterus or the vasa deferentia, occur in the distribution of the nerves from the 

 lower portion of the cord. The administration of certain poisons, such as picro- 

 toxin, has a similar effect. In animals with the medulla oblongata divided, 

 rhythmic respiratory movements can even be induced in this way, if the spinal 

 cord has been previously rendered highly irritable by the administration of strych- 

 nin or the action of heat. 



Also mechanical stimuli are capable of irritating the ganglion-cells 

 of the anterior horns, and, according to Biedermann, the gray matter 

 responds to electrical stimulation. 

 47 



