CONTROL OF PERIPHERAL CIRCULATION 
Head and trunk skin. There is little information about the in- 
nervation of skin in the head and trunk, mainly because of the great 
technical difficulty of estimating cutaneous blood flow in these areas 
with precision. An attempt has been made, however, to study the 
vasomotor innervation of these parts using skin temperature changes 
to estimate blood flow changes in the skin (Blair, Glover, and Roddie, 
1961a). The use of skin temperature as measure of skin blood flow 
has well known limitations. The relationship between the two quan- 
tities is not linear, and at high skin temperatures large increases 
in blood flow can occur without increases in skin temperature. Where 
the skin overlies a large mass of tissue, the skin temperature may 
reflect the temperature of the tissue mass more than the circulation 
through the skin. In addition, changes in skin temperature may re- 
flect changes in the circulation distal to the site of measurement ex- 
cept when the measurement is made at the extremities. Nevertheless 
the method has the merit of simplicity, so that observed differences 
in skin temperature are unlikely to be due to instrumental or tech- 
nical difficulties. This facilitates comparison of circulatory changes 
in symmetrical skin areas on both sides of the body. 
It was found that nose skin behaved rather like finger skin; 
cooling the body caused a much larger fall in the nose and finger 
skin temperature than in body temperature, indicating active vaso- 
constriction in these areas. In the ear, cheek, chest, and forehead 
there was no evidence for vasoconstriction during cooling. When the 
body was heated, however, evidence of vasodilation was found in 
all these skin areas. When the vasomotor nerves to the ear were 
blocked, there was a large increase in skin temperature, and the in- 
crease in ear temperature during body heating did not exceed this 
level (Fig. 17). It was concluded that the changes in ear blood flow 
subserving temperature regulation are mainly due to alterations in 
vasoconstrictor tone. In the cheek and chest, cutaneous nerve-block 
did not alter skin temperature yet reduced the rise in skin tempera- 
ture normally seen during body heating (Fig. 18). It was concluded 
that the vasodilation in these areas is not due to release of vaso- 
constrictor tone, but rather to an active vasodilator mechanism 
mediated through fibres running with the cutaneous nerves. 
This work is still incomplete and is unsatisfactory in many 
respects. Most of the skin in the body is still uncharted as regards 
133 
