CONTROL OF PERIPHERAL CIRCULATION 
cutaneous vasodilation in the forearm during body heating, unlike 
that in the hand, is not due to release of vasoconstrictor tone, but 
rather to an active vasodilator mechanism, mediatedthrough fibres 
running with the cutaneous nerves. It has recently been shown that 
the vasomotor innervation of upper arm, calf, and thigh skin is 
qualitatively similar to that in the forearm (Blair, Glover, and 
Roddie, 1960), but there is no evidence that the vasomotor fibres 
to these areas are involved in any but temperature regulatory 
reflexes. 
Hand skin. The bloodvessels in the hand are normally subjected 
to a high degree of vasoconstrictor tone. Blocking the nerves to the 
hand with local anesthetic normally increases the blood flow through 
the hand from its normal range of about 3 to 10 ml to about 30 to 40 
ml/lOOml/min (Fig. 15). Body heating causes a large reflex vaso- 
dilation in the hand , but this increase can be explained entirely by 
release of vasoconstrictor tone. Despite the evidence for vasodilator 
innervation to the hands of patients with Raynaud's disease (Lewis 
and Pickering, 1931), careful investigation has failed to provide any 
evidence that such fibres are activated during body heating in nor- 
mal individuals. During heating the blood flow in a normal hand 
does not exceed that in a nerve-blocked hand (Arnott and Macfie, 
1948; Gaskell, 19 56; Roddie, Shepherd, and Whelan, 1957c) and atro- 
pinization of the hand does not reduce the vasodilation (Gaskell, 
19 56; Roddie, Shepherd, and Whelan, 19 57b). 
It seemed possible that the body of the hand might show an inter- 
mediate stage between the fingers, with predominantly vasoconstric- 
tor innervation, and the forearm skin, with predominantly vasodilator 
innervation. Experiments of the type described above were therefore 
carried out, in which blood flow through the body of the hand was 
measured by venous occlusion plethysmography, the circulation 
being arrested by rubber bands at the base of each digit (Fig. 16). 
However, the body of the hand behaved as did the whole hand (Roddie, 
Shepherd, and Whelan, 1957b). The skin of the hand seems to function 
as a distinct unit in regard to vasomotor innervation and there is an 
abrupt transition to a different type of vasomotor control somewhere 
about the wrist. 
However, acetylcholine has been obtained from extracts of 
human digital arteries and cholinesterase has been identified in 
129 
