RODDIE, I. C. 
seemed justified. However, appropriate experiments showed that this 
was not the case. Using venous occlusion plethysmography to 
measure forearm blood flow, Barcroft, Bonnar, Edholm and Effron 
(1943) found that blockingthe motor nerves to the forearm with local 
anaesthetic increased flow two to three fold. This increase did not 
seem to be in skin since it was seen even when the cutaneous circu- 
lation was suppressed by iontophoresis of epinephrine into the skin. 
Blocking only the cutaneous nerves to the forearm did not increase 
flow. From these and other control observations it was concluded 
that skeletal muscle is normally subjected to appreciable vasocon- 
strictor tone and that the fibres concerned were distributed to the 
muscle in the motor nerves. 
It was not clear at thattime what role these fibres played in the 
normal regulation of the circulation. Reflex changes in forearm 
blood flow were known to occur during body heating (Wilkins and 
Eichna, 1941). Barcroft, Bonnar and Edholm (1947) found that 
attempted suppression of the cutaneous circulation in the forearm 
by the epinephrine iontophoresis technique failed to prevent the re- 
flex vasodilatation during body heating. They concluded that release 
of vasoconstrictor tone in muscle contributed to this vasodilatation. 
However, in 1952, McGirr found that the rate of clearance of 
Na from human muscle did not increase during body heating. This 
result could not be reconciled with those of the plethysmographic 
experiments unless it were postulated that vasodilatation occurred 
in 'non-metabolic' vessels. This was not a very satisfactory state 
of affairs and further work on the subject became necessary, 
Barcroft, Bock, Hensel, and Kitchin (1955) used heated thermo- 
couples to estimate muscle blood flow. They found that forearm flow 
did not increase during body heating; a fall was the usual finding. 
Roddie, Shepherd and Whelan (1956) used changes in the oxygen 
saturation of effluent venous bloodfrom skin and muscle to estimate 
simultaneously the contribution of these tissues to the vasodilatation. 
Though the oxygen saturation of skin blood rose to almost full satur- 
ation, there was no significant rise in that from muscle (Fig.l). Im- 
provement in the technique for iontophoresis of epinephrine into 
forearm skin allowed Edholm, Fox, and Macpherson (1956) to pro- 
duce more effective suppression of the skin circulation than had 
been obtained in earlier experiments (Barcroft, Bonnar, Edholm, and 
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