348 S. W. RANSON AND P. R. BILLINGSLEY 
irradiation of nervous impulses to other cells of the ganglion. And the 
nerve cells which cannot then be brought into action may be nerve 
cells of the same class as the cells which are in a state of excitation. 
Of this we may give an example. In the cat, at times, when the ar- 
rangement of nerves is posterior, the fourth lumbar nerve causes erec- 
tion of hairs on the tip of the tail; the nervous impulses pass through 
nerve cells in the coceygeal ganglion; other nerve cells in the coceygeal 
ganglia will, on stimulation cause erection of hairs in the greater part 
of the rest of the tail; but no stimulation of the fourth lumbar nerve 
will affect this region. Hence, pilomotor nerve cells, set in action by 
the fourth lumbar nerve, send no commissural fibers to the other pilo- 
motor nerve cells of the coceygeal ganglion. (Langley, ’00.) 
It thus appears that there is no physiological evidence indi- 
cating that diffusion of nerve impulses occurs in the sympathetic 
ganglia and in certain cases, like those cited, there is positive 
evidence that diffusion does not occur. We shall now see that 
there is no histological evidence of any mechanism which could 
serve to bring about such diffusion. 
We may picture such a diffusion mechanism in three ways. 
The first that suggests itself is a diffuse network formed by 
anastomosing branches of the preganglionic fibers. Such a 
network has been assumed by Michailow (11), but without 
adequate evidence. In this respect his description of the inter- 
cellular plexus does not coincide with that given by Dogiel and 
Huber. Very clear pictures of the intercellular plexus are ob- 
tained in pyridine silver preparations, and these give no indication 
of anastomosing fibers or of a closed network. The histological 
evidence is therefore distinctly against the existence of this sort 
of mechanism for diffusion of nerve impulses. 
In the second place, the purpose of diffusion might be served 
by purely intraganglionic neurones whose axons would branch 
repeatedly and end within the ganglion. So far as we have been 
able to find, no one has ever described an axon of a sympathetic 
ganglion cell as ending within the ganglion where it began. 
Wherever axons have been traced they have always been seen 
to leave the ganglion through one or other of its branches. The 
intercellular plexus of fine fibers, which Dogiel and Huber thought 
represented the ramifications of such axons, and which, if inter- 
rupted in this way, might serve as a mechanism for diffusing 
