vi SYMPATHETIC SYSTEM 367 



of the thoracic and higher lumbar nerves, which, when stimulated, 

 yield a sympathetic reaction (supra). 



Langley concludes that the .sympathetic nerve-fibres take origin 

 from a limited region of the cord, and reach the white rami 

 couinumicantes as medullated fibres. This region is the same as 

 that from which the nerves to the trunk emerge, and lies between 

 the regions from which the nerves for the fore- and hind-limbs 

 originate, though overlapping them to a certain extent. The 

 exact limits of the sympathetic origin vary slightly in animals of 

 the same species. 



According to recent researches (Gaskell, Mott, Sherrington, 

 Onuf and Collins, Anderson, Scaffidi, Hering) the spinal cells 

 from which the efferent sympathetic fibres spring lie in the lateral 

 horns, and contribute the so-called intermedia- lateral tract of 

 Lockhart Clarke. 



If we follow the sympathetic fibres along the white rami 

 communicantes in the peripheral direction we meet in the first 

 place the lateral or vertebral ganglia. This opens up the 

 important question as to the relations between the fibres of spinal 

 origin and the elements of these ganglia, more particularly the 

 ganglion cells. 



If the sympathetic fibres behaved like the other efferent fibres 

 of the body, they would pursue an uninterrupted course to the 

 organs which they innervate. We shall, however, find a funda- 

 mental difference in this respect between the two classes of nerve- 

 fibres, as was first established by Langley. 



The two methods commonly employed to determine the peri- 

 pheral course of the fibres observation of the effects of stimulation 

 and study of the degenerations after division are not suit- 

 able for this purpose. No salient qualitative difference has been 

 observed in the effects of exciting the sympathetic fibres above 

 and below the ganglion. And the degeneration method, however 

 valuable elsewhere, is not applicable to the sympathetic system 

 because its fibres are largely non-medullated, and that method is 

 based on the degeneration of the rnyelin sheath (Langley). 

 Observation of a nerve-fibre that was medullated as far as the 

 ganglion, and non-niedullated afterwards, might lead to the false 

 induction that the fibre terminated in the ganglion, since the 

 process of degeneration cannot be followed beyond that point. 

 Nevertheless the experiments with this method have yielded 

 results that agree with those we are now about to consider. 



Langley discovered and elaborated a third method, which is of 

 the utmost importance in determining the different nerve paths, and 

 the constitution of the sympathetic system. This is the nicotine 

 method, based on the property that nicotine has of paralysing the 

 ganglion cells of the sympathetic system, or more probably their 

 synaptic junctions, while leaving the fibres unaffected. 



