INFLUENCE OF TEMPERATURE. 297 



Influence of Temperature on the Capillary Circulation. 

 Within moderate limits, a low temperature, induced by local 

 applications, has been found to diminish the quantity of blood 

 sent to the capillaries, and retard the circulation; while a i 

 high temperature increases the supply of blood and acceler- \ 

 ates its current. The mechanism of this is beautifully shown 

 by the experiments of Poiseuille. This observer found that 

 when a piece of ice was applied to the web of a frog's foot, 

 the mesentery of a small warm-blooded animal, or any part 

 in which the capillary circulation can be observed, the quan- 

 tity of corpuscles circulating in the arterioles became very 

 much diminished, "those which carried two or three rows 

 of corpuscles giving passage to but a single row." The cir- 

 culation in the capillaries first became slower, and then en- 

 tirely ceased in parts. On removing the ice, in a very few 

 minutes the circulation regained its former characters. 



If, on the other hand, the part be covered with water at 

 104, the rapidity of the current in the capillaries is so much 



perfect. The most remarkable case of this kind is one reported by Dr. Houston 

 in the Dublin Journal of Medical Science (1836, vol. x., p. 204). In this case 

 there was a perfect twin, but two distinct cords and sets of membranes. Dr. 

 Houston supposed that the circulation in this monster was carried on by " capil- 

 lary power" alone. In these cases, as has been shown by Astley Cooper and 

 Lallemand (Edinburgh Medical and Surgical Journal, 1844, vol. Ixii., p. 156 et 

 seq.\ there is a free anastomosis of the vessels of the two foetuses in the placenta. 

 Some have supposed, from the fact that the veins of the monster are not provided 

 with valves, that in it the circulation is from the veins to the arteries, or is inverted. 

 It is not exactly clear how the circulation is carried on in an acardiac foetus. Un- 

 doubtedly the heart of one child may influence the circulation in the umbilical 

 vessels of the other, in cases of twins ; for Lallemand has observed (loc. cit.), after 

 the birth of one child, the cord having been divided, a regular pulsatile flow from 

 the placental extremity of the cord, as from a divided artery ; but we find on 

 careful examination of the case reported by Dr. Houston, and an article on the 

 case by Dr. G. Calvert Holland (Edinburgh Med. and Surg. Journal, loc. cit.}, no 

 sufficient evidence that the circulation was carried on by any " capillary power." 

 Not being able to regard as facts these grounds, on which some have based their 

 belief in the existence of a force in the circulation which is independent of the 

 heart's action, we have abstained from their discussion in treating of the causes 

 of the capillary circulation. 



