376 PHYSIOLOGY CHAP. 



the pupil is not further dilated if the nerves to the sphincter are 

 cut on one side or the other of the ganglion. 



Accordingly it is not possible to demonstrate that either the 

 superior cervical ganglion or the ciliary ganglion have any 

 constant tonic influence. Still less can this be proved, as Langley 

 says, for the other peripheral ganglia of the sympathetic. Nor 

 is this surprising seeing that all the known tonic influences 

 exerted by the central nervous system invariably take place 

 reflexly, while the sympathetic ganglia are unable, as we have 

 seen, to subserve reflexes independently of the cerebrospinal axis. 



As the sympathetic ganglia are therefore incapable of sub- 

 serving reflex acts and of maintaining tone apart from the central 

 nervous system, what is their function ? It must be confessed 

 that in the actual state of knowledge a complete answer is not 

 possible. That their function is of importance is beyond doubt, 

 because the animal economy has no superfluous or useless elements ; 

 and observations are not wanting to show that the removal of a 

 ganglion is by no means without injurious effects. Thus, if the 

 cervical sympathetic is cut on the one side, and the superior 

 cervical ganglion is removed on the other, the pupil on this side 

 gradually becomes larger than that of the other side (LangendorfFs 

 paradoxical dilatation of the pupil). There is no satisfactory 

 explanation of this phenomenon, but it shows the influence of the 

 ganglion. 



Langley holds that the sympathetic ganglia are centres of re- 

 inforcement for the central nervous system, and if separated from 

 the latter lose their capacity for carrying out their functions. But 

 it must be remembered that the peripheral ganglia are capable of 

 surviving for years after their separation from the cerebrospinal 

 axis, and of reacting to poisons, or to internal secretions of the body, 

 as those coming from the glandular substance of the paraganglia, 

 which (see Vol. II. Chap. I.) seem from recent researches to have a 

 special affinity for these sympathetic nerve-cells. 



Schultz too suggested that the ganglia may be relays, in which 

 excitations coming from the higher centres by way of the pre- 

 ganglionic fibres are reinforced. 



In addition to this vague and far from well-grounded hypothesis 

 that the peripheral ganglia of the sympathetic are relays for re- 

 inforcement, another theory as to their function, based on their 

 special structural relations, has been put forward. Bidder and 

 Volkmann (1842) pointed out that the number of the nerve-fibres 

 issuing from a ganglion (Langley's post-ganglionic fibres) exceeds 

 the number of fibres entering it (pre-ganglionic fibres) ; this also 

 agrees with the observation referred to above, that one pre-ganglionic 

 fibre may form relations with a number of peripheral ganglion 

 cells. These facts suggest that one function of the ganglia may be 

 to enlarge the field of distribution of the impulses carried towards 



