REGULATING THE CONTRACTIONS OF THE ARTERIES AI 
in the limb. It appears probable that the means by which these concerted 
movements are induced are nerve-cells disseminated through the limb, in the 
same manner as Meissner has lately shown to be the case in the mammalian 
intestine.! The intestines also present a parallel to the arteries, in the fact 
that contractions of their unstriped muscular fibres result from arrest of the 
circulation in them; and I have lately shown? that these movements are not 
due to any influence exerted directly upon the contractile tissue, but that 
the intestinal nerves are essential to their production. Thus we have support 
from analogy for the view that the muscular contractions which occur under 
similar circumstances in the arteries are induced by nervous agency. 
The fact that the contraction produced in an artery of the frog’s web by 
pressure upon a particular point affects a considerable extent of the vessel, 
instead of being limited to the spot irritated, is also an argument for the 
existence of a local co-ordinating apparatus; for I find that this occurrence 
continues to take place in an amputated limb. The observation was made on 
August 4, 1858. One of the hind legs of a frog having been removed after a 
ligature had been passed round the thigh so as to prevent escape of the blood, 
pressure was made with a fine but blunt instrument over a particular point 
in the course of a large artery, whose calibre had previously been accurately 
determined by micrometer. The contractions which resulted affected the 
immediately adjacent parts of the vessel to an extreme degree; the effect, 
however, was not limited to these, but gradually shaded off in both directions ; 
and even at a considerable distance, where by ordinary observation no change 
might have been detected, the micrometer showed a diminution from 6° to 
5°,> occurring immediately upon the irritation and subsiding soon after. 
Similar results were obtained on repetition of the experiment. 
From the analogy of the intestinal and cardiac movements,’ it is probable 
that the local co-ordinating apparatus for the arteries comes into play in all 
cases of arterial contraction in the living animal, and is the medium through 
which the nerves which arise from the cord act upon the vessels. But it is 
very important to bear in mind that it is, under ordinary circumstances, in 
entire subjection to the spinal system, and only acts independently under 
special conditions of local irritation. 
It remained as yet undecided whether the nervous centre for the arteries 
contained in the cerebro-spinal axis were extensively diffused or limited to 
* Henle and Pfeufer’s Zeztschrift, 2nd series, vol. viil, 1857 
* Vide ‘ Preliminary Account of an Inquiry into the Functions of the Visceral Nerves, &c.’ (p. 90 of 
this volume). 
* These degrees have a different value from those mentioned in other parts of this paper, a different 
micrometer having been employed. * See ‘ Preliminary Account, &c.’, before referred to. 
