THE THIRD HUXLEY LECTURE 519 



vessels — arteries, capillaries, and veins — had disappeared ; the field being 

 absolutely exsanguine. In a short time the circulation was resumed with 

 greater freedom than ever ; and on repeating tlie experiment I found that the 

 first effect of the stimulus was a state of extreme constriction of the arterioles, 

 which kept back the blood-corpuscles but allowed the liquor sanguinis to pass ; 

 so that the capillaries and veins, though retaining their former dimensions, 

 were occupied only by the filtered plasma, itself invisible, while their walls 

 were with difficulty discernible under the low magnifying power that I w^as 

 using. 



Thus was swej^t away at one stroke the latest theory upon the subject. 

 The condition of contraction of tlie arterioles, which Wharton Jones had 

 supposed to be the cause of the accumulation of the red corpuscles in the 

 capillaries, had been present in the most perfect conceivable form ; but the 

 result had been the very opposite condition. 



The explanation of Wharton Jones's mistake became apparent as I pro- 

 ceeded along the path which opened with so much promise. He had never 

 experimented in a perfectly healthy state of the circulation, but had described 

 with great accuracy what could occur only under morbid conditions. Eor 

 I afterwards learned that the normal temperature of man is deadly to the 

 cold-blooded frog. That animal, which under ordinary conditions exhibits 

 very remarkable persistence of vitality even after somatic death, is killed by 

 being held for about a quarter of an hour in the hand ; and if one of its hind 

 feet be similarly warmed, the blood-corpuscles will be found packed and 

 stagnant in the vessels of the webs, as if mustard or any other powerful 

 irritant had been applied to them. 



If, on the other hand, in securing the frog for observation under the micro- 

 scope, scrupulous care was taken to avoid needless exposure of the foot to the 

 warmth of the hands, the threads for fixing the toes being tied by means of long 

 forceps, and each half of the knot done separately, with a fair interval between 

 them, a state of the circulation was seen which is, I believe, even to this day 

 rarely witnessed. The white corpuscles, instead of trailing, more or less 

 sluggishly, along the walls of the venous radicles — the normal condition, ac- 

 cording to some modern textbooks — move freely along among the red discs, 

 and these being diffused through a due proportion of licjuor sanguinis, the 

 vessels present a pallor which would surprise any one who had seen only the 

 ordinary demonstrations of the circulation, but wliich might liave been anti- 

 cipated from the appearance, when in liealth, of the highly vascular sclerotic 

 with its investing conjunctiva, * the white of tlie eye '. 



Such a method of arranging the foot could not bo carried out il the animal 



