152 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



to a constant inflow of impulses along the seinsory paths. The 

 muscle tonus, in other words, is really a reflex tonus, which differs 

 from ordinary reflex movements only in the absence of a sudden, 

 visible contraction and in the more or less continuous character 

 of the innervation. The idea of a more or less continuous but 

 varying activity of the centers in the brain and cord in conse- 

 quence of the constant inflow of impulses along the sensory paths 

 fits in very well with many facts observed in the peripheral organs 

 — facts that will be referred to from time to time as the physiology 

 of these organs is considered. 



Effects of Removal of the Spinal Cord. — Numerous investi- 

 gators have sectioned the cord partly or completely at various 

 levels. The general results of these experiments as regards loss 

 of sensation or voluntary movement are described in the next 

 section treating of the cord as a path of conduction to and from 

 the brain. But attention may be called here to some of the gen- 

 eral results obtained by Goltz * in some remarkable experiments 

 in which the entire cord was removed with the exception of the 

 cervical region and a small portion of the upper thoracic. In 

 making this experiment it was necessary to perform the operation 

 in several steps. That is, the cord was first sectioned in the upper 

 thoracic region and then in successive operations the lower tho- 

 racic, lumbar, and sacral regions were removed completely. Very 

 great care was necessary in the treatment of the animals after 

 these operations, but some survived and lived for long periods, 

 the digestive, circulatory, and excretory organs performing their 

 functions in a normal manner. The muscles of the hind limbs 

 and trunk, however, underwent complete atrophy, owing to the 

 destruction of their motor nerves. The blood-vessels also were 

 paralyzed after the first operations, but gradually their muscu- 

 lature again recovered tone, showing that, although under normal 

 conditions the tonic contraction of the vessels is under the in- 

 fluence of nerves arising from the cord, this tone may be re-estab- 

 lished in time after the severance of all spinal connections. Some 

 of the specific results of these experiments, bearing upon the re- 

 flexes of defecation, micturition, and parturition, will be described 

 later. Attention may be called here to the general results 

 illustrating the general functions of the cord. 



In the first place, there was, of course, a total paralysis of volun- 

 tary movement in the muscles innervated normally through the 

 parts of the cord removed, and a complete loss of sensation in the 

 same regions, particularly of cutaneous and muscular sensibility. 

 In the second place, the visceral organs, including the blooa- vessels, 



* Goltz and Ewald, "Pfliiger's Archiv fiir die gesammte Physiologie," 63,. 

 362, 1896. 



