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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



Reactions to Injury 



mechanical injury. The reactions to mechanical 

 injury were very completely studied by Lewis ( 1 39). 



The while reaction. When warm skin is lightly stroked 

 with a blunt point there is a temporary blanching as 

 blood is expressed from and then returns to the super- 

 ficial vessels. About 1 5 sec later, the line of the stroke 

 becomes pale again, the pallor reaching its maximum 

 about 30 sec after the stroke, and fading in about 3 

 to 5 min. The white line is sharply localized to the 

 area stroked. Its development is unaffected by the 

 temporary arrest of the circulation, and it was there- 

 fore taken by Lewis to indicate active contraction of 

 the vessels responsible for the color of the skin, and 

 not merely deprivation of these vessels by contrac- 

 tion of the arterioles that supply them. The vessels 

 responsible for color are able to sustain their con- 

 traction against a distending pressure of 80 to 100 

 mm Hg produced by venous congestion. 



The triple response. When the stroke is much or very 

 much firmer, the white reaction is replaced by a 

 different response which, when fully developed, has 

 three components, the red line, flare, and wheal, a) 

 The most constant component is a sharply de- 

 marcated red line which develops along the line of 

 the stroke with a latency of 3 to 15 sec, and the in- 

 tensity and duration of which increase with the 

 strength of the stimulus. Like the white reaction, the 

 red line develops even when the circulation is tem- 

 porarily arrested. It was considered by Lewis (139) 

 to indicate active dilatation of the vessels responsible 

 for the color of the skin, b) In susceptible skins, and 

 with strong or repeated stimuli, an irregular red 

 flare develops about 15 to 30 sec after the red line, 

 and gradually extends for 2 to 3 cm on each side of 

 the line of the stroke. The flare remains a bright 

 scarlet color, unlike the red line which becomes 

 progressively dusky. As the flare fades, it becomes 

 mottled. A white reaction can be developed across 

 the flare by light stroking, but not across the red 

 line. The flare was considered by Lewis (139) to 

 indicate arteriolar dilatation, c) In sensitive skins, 

 or in others following a strong stimulus such as the 

 lash of a whip, a raised wheal usually begins to appear 

 along the line of stroke in 1 to 3 min, reaching full 

 development in 3 to 5 min. It overlies the red line 

 and the line becomes pale, presumably because of 

 the pressure exerted by the transuding fluid upon 

 the minute vessels. 



The triple response is unaffected when the sensory 

 nerves are freshly interrupted by section or local 



anesthesia. The red line and the wheal continue in 

 chronically denervated skin, but the flare is lost after 

 about the sixth or seventh day when the sensory 

 nerves degenerate. This led Lewis (139) to conclude 

 that the red line and wheal are independent of nerves, 

 but that the flare depends on a local axon reflex (49). 

 The nerve impulse arises in a receptor in the skin 

 and, after ascending a sensory nerve for some distance, 

 returns antidromically along a branch to arrive at an 

 arteriole and cause it to dilate. 



The triple response is the standard reaction of the 

 skin to a great variety of injurious stimuli. The re- 

 sponse to mechanical trauma can be exactly repro- 

 duced by pricking histamine into the skin. Further, 

 if trauma or a histamine prick is applied while the 

 circulation is arrested the development of the flare 

 is delayed until the circulation is released. This and 

 other evidence led Lewis (139) to postulate that the 

 flare depends on the activation of the skin receptors 

 by an H-substance, which may be histamine, rather 

 than directly by the mechanical trauma. 



ultraviolet light. Irradiation with ultraviolet 

 light, which penetrates to a very small depth in the 



fig. 8. Two experiments. Hand blood How in ml/ 100 ml/ 

 min. Solid circles: injected arm; open circles: control arm. The 

 heights of the vertical columns indicate the percentage satura- 

 tion of venous blood with oxygen. Intra-arterial injection of 5 

 ml of nitrous oxide is indicated by the black rectangle starting 

 at o min. [From Duff el at. (67).] 



