1120 PHYSIOLOGY 



the sympathetic ganglion-cells are paralysed by nicotine (Langley). 

 The nicotine may be painted on the ganglion or may be injected into 

 the blood-stream. The first effect of the drug is a powerful stimula- 

 tion of the ganglion-cells, so that, if the drug be injected, there is an 

 enormous rise of blood pressure owing to the universal vaso-con- 

 striction that is produced. The stimulation gives place to a condition 

 of paralysis ; the blood pressure falls below normal, owing to the 

 cutting off of the peripheral vascular nerves from the vaso-motor centre. 

 Stimulation of the pre-ganglionic fibre is now without effect, although 

 the normal results follow stimulation of the post-ganglionic non- 

 medullated fibre. 



By these methods it has been determined that all the vaso-con- 

 strictor nerves of the body leave the spinal cord by the anterior roots 

 of the spinal nerves from the first dorsal to the third or fourth lumbar 

 inclusive. From the roots they pass by the white rami communicantes 

 to the ganglia of the sympathetic chain lying along the front of the 

 vertebral column. Here they take different courses according to their 

 destination. 



The fibres to the head and neck leave by the first four thoracic nerves, 

 pass into the sympathetic chain through the ganglion stellatum and 

 ansa Vieussenii to the inferior cervical ganglion, and up the cervical 

 sympathetic trunk to the superior cervical ganglion. Here they end, 

 and the impulses are carried by a fresh relay of fibres, which start from 

 cells in this ganglion and travel as non-medullated fibres on the walls 

 of the carotid artery and its branches. 



The constrictors to the fore limb in the dog leave the cord by the 

 white rami of the fourth to the tenth thoracic nerves. The fibres run 

 up the sympathetic chain to the stellate ganglion, where they all end 

 in synapses round the cells of this ganglion. The impulses are carried 

 on by non-medullated fibres along the grey rami of the sympathetic 

 to the cervical nerves which make up the brachial plexus, and run 

 down in the branches of this plexus to be distributed to the vessels 

 of the fore limb. 



The constrictor impulses to the hind limb in the dog arise from 

 the nerve-roots between the eleventh dorsal and third lumbar roots. 

 All the fibres end in connection with cells in the sixth and seventh 

 lumbar and first and second sacral ganglia of the sympathetic chain, 

 whence the impulses are carried by grey rami to the nerves making 

 up the sacral plexus. 



The most important vaso-motor nerve of the body is the splanchnic 

 nerve. This nerve receives most of the fibres forming the white rami 



^ the lower seven dorsal and upper two or three lumbar roots, the 



- a ,s often taking a separate course as the lesser splanchnics. 



^.n be seen to pass through the sympathetic chain of the 



