TONIC FUNCTIONS OF THE CORD. 869 



the so to say resting condition of their spinal centres a certain 

 tension and contraction sufficient to offer resistance to the opening of 

 the orifices they surround. Depression of function of the spinal cord, 

 e.g. in spinal shock, diminishes greatly, at least for a time, the tonic 

 contraction of the sphincter muscles. Destruction of the cord renders 

 the orifices for a time patulous. 1 Similarly, the tonic contraction of 

 the vascular musculature is for a time 2 decreased by section of spinal 

 nerves or destruction of the spinal cord ; lateral semisection of the cord 

 in the neck is followed by more or less permanent narrowing of the 

 homonymous pupil. Section of the vagus produces in the dog an 

 increased frequency of heart-beat. These phenomena, like the rhythmic 

 discharges of the respiratory centre, point to a continued activity of the 

 bulbo-spinal centres, probably in result of some extrinsic, constant, or 

 frequently repeated stimulus. The tonic action of some of the spinal 

 efferent root cells that embouch into the sympathetic, although marked, 

 is not apparently so dependent on the afferent root cells of their own 

 locality as is that of the motor root cells innervating skeletal mus- 

 culature. I have repeatedly found no perceptible difference in size 

 between the pupils, after complete section of all the afferent roots of one 

 side in the cilio-spinal region ; nor when the cervical sympathetic has 

 been cut weeks subsequent to complete spinal transection at the seventh 

 cervical level. I have seen careful section of all the afferent roots of 

 both sides, from the second thoracic to the thirteenth inclusive (cat), 

 leave the arterial pressure practically unaltered. In accord with such 

 observations is the greater difficulty of obtaining, from the second and 

 third thoracic afferent roots in the spinal mammal, a pupillar dilatation 

 than a contraction of the skeletal musculature. 



As with other centrifugal nerve discharges, especially with rhythmic- 

 ally recurrent, there arises the question here whether the initiation is 

 peripheral and reflex, or whether autocthonous and outcome of the 

 independent individual metabolism of the nerve cells that themselves 

 discharge. The rhythmic explosion in the muscle cells of the heart 

 and their tonicity, expression of a more continuous discharge, seems 

 shown autocthonous in origin. So also, among nerve cells, the explosive 

 discharges of the bulbar respiratory seem to offer counterpart to that 

 of cardiac cells among the muscular. In some instances the tonus of 

 spinal nerve cells may be autocthonous in origin, evolved by " inner 

 stimulation " of the " centre " itself. In other instances, spinal neural 

 tonus is distinctly of peripheral initiation and demonstrably reflex. 



The resting length of an innervated muscle varies. 3 The bladder 

 accommodates itself to various volumes of contents. 4 If urination 

 be deferred, when need is felt, the feeling of need will pass by, 

 and Mosso found the intravesical tension then fall to that which 

 previously obtained under a much smaller content of urine. The 

 need for micturition felt at waking is perhaps chiefly due to increase of 

 tension resulting from increase of neural tonus, as the activities of the 

 cord return with the general awakening of the nervous system. 



1 Cf. Goltz and Ewald, Arch. /. d. gcs. Physiol., Bonn, 1896, Bd. lxiii. S. 362; 

 Kronecker and Arnold, Rep. Brit. Ass. Adv. Sc, London, 1899. 



2 Goltz, Arch. f. d. ges. Physiol., Bonn, Bd. ix. S. 174, etc. 



3 Tschiriew, Arch. f. Physiol., Leipzig, 1879 ; v. Anrep, Arch. f. d. gcs. Physiol., Bonn, 

 1880, Bd. xxi. S. 226. Cf. also Cyon, Per. d. k. Sachs. Gesellsch. d. Wissensch., math.- 

 phys. CL, Leipzig, 1865. 



4 A. Mosso and Pellacani, Arch. ital. de biol., Turin, 1881, tonio i. pp. 96, 291. 



