xv INTRODUCTION 
The vascular reaction to irritation was found by Lister, as has been said, 
to be indirectly produced through the medium of the central nervous system. 
That the calibre of the arteries was controlled by the nervous system had 
recently been established by Claude Bernard’s discovery that section of the 
cervical sympathetic was followed by dilatation of the blood-vessels in the 
head and neck, and Waller’s observation that stimulation of this nerve caused 
constriction in the same area. Waller and Budge also had just shown that 
the fibres of the cervical sympathetic, stimulation of which occasioned con- 
striction of the vessels, emanated from the upper dorsal region of the spinal 
cord. On the other hand, Wharton Jones had stated that whilst division of 
the sciatic nerve was followed by extreme dilatation of the vessels in the 
frog’s web, section of the roots of the sciatic within the spinal canal failed to 
produce this effect, whence he inferred that the constrictor fibres in the sciatic 
trunk came not from the cord but from the ‘Sympathetic system’. 
Lister, who was no doubt interested in the control of the calibre of the 
blood-vessels primarily on account of his observations upon the vascular reaction 
in inflammation, proceeded to make an investigation to ascertain which parts 
of the nervous system regulated the contraction of the arteries,! with the 
view of clearing up the apparent discrepancy suggested by the observations 
of Waller and Budge and Wharton Jones respectively. 
The experiments were made upon the frog, and the size of the vessels of 
the web directly observed and measured by an eyepiece-micrometer. Both 
webs were simultaneously under observation, sothat when the nervous connexions 
of the one side were interfered with, the other served as a control. With this 
simple technique he conducted a series of experiments, which even at the 
present time could not fail to excite admiration on account of the simple 
directness of their conception and the ingenuity with which they were carried 
out. He showed how Wharton Jones was led to a false conclusion, and estab- 
lished the fact that the fibres controlling the calibre of the vessels in the web 
of the frog issue from the spinal cord, as do those through which sensation 
and motion are effected in the hind limbs. He further demonstrated that the 
greatest focus whence those fibres emerged was at the posterior end of the cord, 
so that if this portion of the spinal axis were removed, intense dilatation ensued. 
Unless, however, the amount of cord removed was extensive, after an interval 
of some days the vessels recovered to some extent their former calibre, showing 
that the supply is not absolutely confined to any limited region. Experiments 
on frogs in which the whole nervous system had been destroyed, and upon 
amputated limbs also, led him to conclude that there must in addition be © 
1 Vol. 1, p27. 
