CIRCULATION THROUGH THE SKIN 



'333 



fic. 5. Reaction of arteriovenous 

 anastomoses in the rabbit's ear to local 

 cooling, 0, before and b, during cooling. 

 .4, artery, !', vein; AV, arteriovenous 

 anastomosis, closed in a and open in b. 

 [From Grant (98).] 





Mkk Ski Oil 



LIBRA 



Mi M Hi 



60 o 



MINUTES 



60 O 



60 



fig. 6. The heat loss in cal/100 ml/min from the R and L index fingers to water in the range 

 0-6 C with intervals of o min (left), 5 min (middle), and 10 min (right) between their insertion 

 into the calorimeters. The full width of the lower frames is 60 min. The clear areas represent heat 

 derived from the tissues of the finger in cooling to calorimeter temperature during the first 6 min 

 of insertion. Pain is represented on a roughly quantitative scale by marks at the top of the frames. 

 The full height of the frame corresponds to a blood flow of not less (1 10) than 80 ml/100 ml of 

 finger/min. [From Greenfield el al. (109).] 



cluck. The arteriovenous anastomoses in the rabbit's 

 ear (fig. 5) were directly seen by Grant (98) to dilate 

 to cold. In the hands and feet, and particularly in 

 the digits, the intensity of the cold vasodilatation was 

 found by Grant & Bland (99) to parallel closely the 

 density of the arteriovenous anastomoses, and it seems 

 likely that the dilatation of the latter is mainly re- 

 sponsible for the increased blood flow. 



Subsequent calorimetric observations (16, 105) 

 have shown that for the first 5 to 10 min of immersion 

 in ice cold water there is a constriction of the vessels 

 with almost complete arrest of blood flow (fig. 6). 

 At this time there is a considerable degree of pain. 

 The vessels then rapidly dilate, the pain goes and the 

 finger feels warm and comfortable. In a warm sub- 

 ject, the blood flow may rise to a value which is 

 probably as high as is attained by any other type of 

 vasodilatation (105). 



With continued immersion, the dilatation is ir- 

 regularly interrupted by periods of constriction 

 lasting a few minutes. These may be abrupt in onset 



and termination, and may cause almost complete 

 arrest of blood flow (108). The pattern and timing of 

 these periods of constriction differ in different digits 

 simultaneously observed, and appears to be locally 

 determined (109). During continued immersion the 

 general level of the peaks of vasodilatation often 

 tends to decline, but if the subject is kept warm, 

 alternation of dilatation and constriction may con- 

 tinue for several hours (37). On removal of a finger 

 from the cold water the dilatation persists, and for 

 about half an hour the finger may be warmer than 

 its nonimmerscd neighbors (192). The vasodilator 

 response is conspicuous on immersion at temperatures 

 near o C, but it is detectable at temperatures as high 

 as 12 C or 15 C. 



The vasodilator response is present after inter- 

 ruption of the sympathetic outflow from the central 

 nervous system by local anesthetic block or by chronic 

 section. It is, however, influenced by sympathetic 

 activity. Among chilled individuals there are con- 

 siderable differences in the response, but the vaso- 



