THE CERVICAL SYMPATHETIC TRUNK 347 
stimulation of a small sensory nerve may bring about reflex 
activity of the skeletal and involuntary musculature over the 
entire body. Are impulses disseminated in a similar way in the 
sympathetic ganglia? Langley (00) maintains that a pregan- 
glionic fiber branches and becomes associated with several 
postganglionic neurones and that these taken together form a 
functionally isolated unit. That is to say, there is no general 
diffusion of impulses through the ganglion. This is beautifully 
illustrated by his experiments on the pupilodilator pathway. 
As pointed out by Hoffmann (’04), the stimulation of a long 
ciliary nerve causes local dilation of the pupil, while stimulation 
of the white ramus of either the first or second thoracic nerve 
causes a general and symmetrical dilation. This might appear 
to be due to a spreading of the impulses within the superior cervi- 
eal ganglion to all postganglionic pupilodilator neurones. This 
is not the case, however, as Langley (04) has shown: 1) Because 
stimulation of a small number of postganglionic fibers as they 
leave the ganglion in any one of the four bundles that form the 
internal carotid nerve will also cause a symmetrical general 
dilation. Fibers from such a bundle undergoing rearrangement 
in the internal carotid plexus are distributed to all parts of the 
iris. It is therefore unnecessary to assume any spreading out of 
nerve impulses through diffusion in the ganglion. 2) Local 
dilation of the pupil can, on the other hand, be obtained by 
stimulating a few preganglionic fibers in one of the rootlets of the 
upper thoracic nerves. It is difficult to see how, on any theory 
of the cells being connected together to form a codrdinating 
center, stimulation of a small number of preganglionic fibers 
could cause rather marked local dilation of the pupil. The spread- 
ing out of the impulses which does occur is due to the intermin- 
gling of the postganglionic fibers in the preterminal plexuses. 
An even more striking case has been made out against the 
general diffusion of nerve impulses within sympathetic ganglia in 
the case of the coccygeal ganglion. 
In all compound ganglia it is obvious that stimulation of certain of 
the preganglionic fibers running to the ganglia excites some only of the 
nerve cells, and no increase in the strength of the stimulus can cause 
