CONTROL OF PERIPHERAL CIRCULATION 
impressions of vasomotor regulation in the body have been gained 
by considering vasomotor responses in the hand to be representative 
of those occurring in other tissues. It is now quite clear that the 
conclusions from experiments on hand skin cannot be extrapolated 
to forearm skin, let alone to the other tissues of the bocfy. For this 
reason it is convenient to consider the innervation of different skin 
areas separately from that of hand skin. 
Forearrn skin . Vasomotor innervation of forearm skin can be 
conveniently demonstrated by the type of experiment illustrated in 
Figure 10. Blood flow was measured by venous occlusion plethys- 
mography in both forearms of a comfortably warm subject. At the 
beginning of the experiment the level of blood flow was similar on 
the two sides. When the cutaneous nerves to one forearm were 
blocked, there was little change in the level of flow on that side 
relative to that on the control side. This indicated that the cutaneous 
vessels are not subjected to any appreciable vasoconstrictor or 
vasodilator tone when the subject is comfortably warm (Edholm, Fox 
and Macpherson, 1957). When the subject was then cooled, by direct- 
ing a fine spray of coldwater over his chest and abdomen, the blood 
flow on the innervated side fell to a lower level than that on the 
nerve-blocked side. This result indicated that cutaneous vessels 
are innervated with vasoconstrictor fibres which are active in 
temperature regulation (Roddie, Shepherd, and Whelan, 1957a). It 
has recently been shown (Blair, Glover, Kidd, and Roddie, 1960) 
that these fibres are adrenergic, since the vasoconstriction of fore- 
arm skin on cooling the body can be prevented by intra arterial 
infusion of bretylium tosylate. 
When a recumbent subject is comfortably warm, the rate of 
blood flow through the forearm is about 4-5 ml/lOOml/m in. Cooling 
the body causes flow to fall to about 1.5 to 2.5 ml/lOOml/min, and 
as indicated above, this reduction is due to activity of vasocon- 
strictor fibres. A reduction of the same order is produced by sup- 
pression of the skin circulation by iontophoresis of epinephrine into 
the skin (Cooper, Edholm, and Mottram, 1955). It is likely, therefore, 
that vasoconstrictor nerves to the forearm skin, like those to the 
hand skin, can stop the flow of blood through the skin tissue 
completely. 
123 
