716 THE SPINAL NERVES. 



of the cranial nerves. Even sensory branches of other sensory nerves may enter 

 also into the trunks of sensory nerves. This fact explains the remarkable ob- 

 servation that, after division of a nerve-trunk, for example the median, its peripheral 

 extremities remain sensitive. Landois offers the simple explanation for the condi- 

 tions described that the tissue of the motor and sensory nerves contains (as do 

 most of the tissues of the body) sensory fibers. 



As a result of carefully observed experiments with division of the roots, as 

 well as after discovery of the reflex relations of the sensory roots to irritation 

 of the anterior root (reflex movement) by Johannes Miiller and Marshall Hall, the 

 following deductions may be readily made from the general law of Bell: (i) At 

 the moment of division of the anterior root a contraction (mechanical irritation 

 of the motor fibers) occurs in the muscles supplied from this root. (2) A sensation 

 of pain, however, also results (recurrent sensibility). (3) After the section the 

 related muscles are paralyzed. (4) Irritation of the peripheral stump of the 

 anterior root causes (in the first period after the operation) contraction of the 

 muscles, eventually also a sensation of pain in consequence of the recurrent 

 sensibility. (5) Irritation of the central stump is entirely without effect. (6) 

 Sensation is completely preserved in the paralyzed parts of the body. (7) Severe 

 pain occurs at the moment of division of a posterior root. (8) A reflex movement 

 occurs at the same time. (9) After the section, all regions supplied by the divided 

 root are anesthetic. (10) Irritation of the peripheral stump of the divided root 

 is without any effect, (n) Irritation of the central stump causes pain and reflex 

 movement. (12) Motility is entirely preserved in the anesthetic parts, for ex- 

 ample the extremities. 



According to Waller, the peripheral portion always undergoes degeneration 

 after division of the anterior root. Division of the posterior root in advance of 

 or behind the ganglion leaves unaltered the peripheral fibers that have retained 

 their connection with the ganglion. Those that are severed degenerate. There- 

 fore, according to Waller, the spinal cord is the nutritional center for the anterior 

 roots, and the spinal ganglion, on the other hand, for the posterior. 



After division of the posterior roots, for example of the nerves for the posterior 

 extremities, the muscles retain their motility, but, nevertheless, characteristic dis- 

 turbances can be recognized in them. These consist in an apparent awkwardness 

 with which the animal executes the movements (jumping about in an uncertain 

 manner, holding the legs far apart in walking, etc.) , which detracts from the normal 

 harmony and elegance centripetal ataxia. Landois observed that dogs in which 

 the posterior roots for the posterior extremities were divided on both sides ex- 

 hibited, after complete recovery in other respects, difficulty in balancing the 

 posterior part of the body, which often fell over in running or in wagging the 

 tail. The phenomena are due to the fact that in consequence of the anesthesia 

 of the muscles and the skin, the animal is unconscious of the resistances opposed 

 to its movements. Therefore, the measure of muscular force to be employed 

 cannot be properly estimated. All aids excited through reflex influences are also 

 naturally excluded. Animals with abolition of sensibility in individual extremities 

 often hold these in abnormal positions, from which the animal with preserved 

 sensibility would at once remove them. Analogous ataxic disorders of movement 

 have been observed also in human beings with degenerated peripheral extremities 

 of the cutaneous nerves. 



Under some circumstances division of the sensory nerves in certain regions 

 may indeed be attended with abolition of movement. In whole-hoofed animals, 

 immobility of the upper lip was observed after resection of the infraorbital nerve, 

 immobility of the corresponding side of the larynx after division of the superior 

 laryngeal nerve, also loss of motility of the esophagus after paralysis of its sensory 

 nerve. The motility is thus, in large measure, dependent upon preservation of 

 the sensory nerves (sensomobility) . 



Harless, Ludwig and Cyon have made the observation, which, however, has 

 been disputed by v. Bezold, Uspensky, Griinhagen, and G. Heidenhain, that the 

 anterior roots possess a greater degree of irritability so long as the posterior remain 

 intact and irritable, that, however, they exhibit signs of lessened irritability as 

 soon as the posterior roots are divided. In explanation of this phenomenon it 

 must be assumed that in the intact body a series of slight irritations pass succes- 

 sively through the posterior roots (from contact, position, the influence of tem- 

 perature upon the parts of the body, and the like), and are transmitted 

 renexly through the spinal cord to the motor roots, so that, as a result, a 

 slighter additional irritation is required in order to excite the anterior roots than 



