HuBER, Sympathetic Nervous System. 117 



All the spinal nerves have grey rami, which, as above 

 stated, consist largely of non-medullated fibers. Since no non- 

 medullated nerves leave the cerebro-spinal axis through ei^er 

 its anterior or posterior root (Gaskell, 79) and since "the first 

 thoracic spinal nerve, the uppermost nerve which has a white 

 ramus, is the uppermost nerve which on stimulation produces 

 sympathetic effect" (Langley, 78) and since, further, the white 

 rami can be traced into the sympathetic ganglia of the chain 

 and the pre-vertebral ganglia, it follows that a stimulus applied 

 to a spinal nerve in the vertebral canal or to the cord itself, pro- 

 ducing a sympathetic effect, excites an impulse which travels 

 along nerve fibers contained in the anterior roots and thence 

 passes through the white rami to the sympathetic ganglia. 



Gaskell (79) expresses this thought in the following lan- 

 guage :— 



"The white rami communicantes are formed by an out- 

 flow of medullated fibers from both anterior and posterior roots 

 of the spinal nerves between the second thoracic and second 

 lumbar inclusive (the fibers from the posterior root are prob- 

 ably sensory as will be explained later), which medullated nerves 

 pass not only into their metameric sympathetic (lateral) ganglia, 

 but also form three main streams, upwards into the cervi- 

 cal ganglia, downwards into the lumbar and sacral ganglia, and 

 outwards into the collateral (pre-vertebral) ganglia." 



" The white rami communicantes alone constitute the rami 

 viscerales of the morphologist. The out flow of visceral nerves 

 from the central nervous system into the so-called sympathetic 

 system takes place by their means alone." 



To bring these points more closely before you, I may describe 

 briefly some of the physiological effects observed in stimulating 

 the cervical sympathetic. It is well known that by stimulating 

 the cervical sympathetic of the dog, cat or rabbit the pupil be- 

 comes dilated, there is an increase in the secretion from the sub- 

 maxillary gland and a constriction of the small vessels of the 

 ear, conjunctiva and other parts of the head. These same 

 changes may be observed on stimulating the superior cervical 

 ganglion directly, or on stimulating some of the nerves given 



