CENTRAL NERVOUS SYSTEM. 655 



It has been observed upon stimulation of the branches of the coeliac plexus 

 in the dog, that the several branches, though unlike in size, bring about nearly 

 the same quantitative reaction, in the constriction of the veins, from which we 

 infer that though entering the peripheral plexus by different channels, the 

 impulses find their way to the same elements at the end, owing to a multi- 

 plicity of pathways within the plexus. 1 



Experiments with strychnin on the more proximal sympathetic ganglia do 

 not show any increased diffusibility following the application of the drug, but 

 on the other hand, Langley and Dickinson 2 have shown that nicotin applied 

 to various sympathetic ganglia of the cat produces a condition whereby elec- 

 trical stimulation below the ganglion, which in the normal animal is followed 

 by dilatation of the pupil, is without effect. Since the application of the drug 

 to the nerve-fibres on either side of the ganglion is ineffective, when at the 

 same time the application to the ganglion itself is effective, it is inferred that 

 the drug acts by altering some peculiar relation existing within the ganglion, 

 and the relation which is assumed to be thus modified is that between the 

 fibres terminating in the ganglion and the cells which they there control. 

 The relation between the post-gauglionic fibres and the peripheral plexuses is 

 not interrupted by nicotin, and hence is different from that between the pre- 

 ganglionic fibres and the cell-bodies which they control. 



Evidence for Continuous Outgoing Impulses. Under normal condi- 

 tions, striped and uustriped muscular tissues are always in a condition of 

 slight contraction. When the nerves controlling any such set of muscles are 

 cut, or their central connections injured, the muscles at first relax. 



If a frog, rendered reflex by the removal of the brain, the cord remaining 

 intact, be hung up vertically, it is found that the legs are slightly flexed at 

 the hip and knee. If now the sciatic nerve be cut upon one side, the leg on 

 the side of the section hangs the straighter, indicating that the muscles have 

 relaxed a little as the result of the section of the nerve ; if, in the same animal, 

 the smaller arteries in the web of the foot be examined both before and after 

 the section, it is found that after the section they have increased in diameter. 

 Conversely, artificial stimulation of the peripheral stump causes a contraction 

 of the vessels, but it is not possible in so rough a way to imitate the tonic con- 

 traction of the skeletal muscles. 



It is inferred from these experiments that normally there pass from the 

 central system along some of the nerve-fibres impulses which tend to keep the 

 muscles in a state of slight contraction. Destruction of the entire cord abolishes 

 all outgoing impulses, and produces a complete relaxation of these muscles. 



Though the intensity of these outgoing impulses is normally always small, 

 yet it is subject to significant variations. The difference between the tone of 

 the muscles of an athlete in prime condition and those of a patient recovering 

 from a prolonged and exhausting illness is easily recognized, and this differ- 

 ence is in a large measure due to the difference in the intensity of the impulses 



1 Mall : Archlvfilr Anatomic und Physiologic, 1892. 



2 Proceedings of the Royal Society, 1889, vol. xlvi. 



