484 OF THE CIRCULATION OF THE BLOOD. 



demonstrated by proper means, that the negative results cannot be admitted as 

 invalidating the fact. It is of course in the smaller arteries, that the evidence 

 of this contractility should be sought ; and this may be readily obtained by 

 observing the effects of various stimuli, mechanical, chemical, or electrical, upon 

 the vessels of a transparent membrane, such as the bat's wing or the frog's foot. 

 Thus if, whilst we watch the movement of blood in a companion artery and vein, 

 we draw the point of a fine needle across them three or four times, without 

 apparently injuring them or the membrane over them, they will both presently 

 contract and close ; then after remaining for a few minutes in the contracted 

 state, they will begin again to dilate, and will gradually increase in diameter 

 until they acquire a larger size than before the stimulus was applied. When in 

 this condition, they will not again contract on the same stimulus as before ; the 

 needle may now be drawn across them much oftener and more forcibly, but no 

 contraction ensues, or only a trivial one which is quickly followed by dilatation ; 

 with a stronger stimulus, however, such as that of great heat, they will again 

 contract and close, and such contraction may last more than a day before the 

 vessels again open and permit the flow of blood through them. 1 The compara- 

 tive effects of chemical and other stimuli have recently been especially studied 

 by Mr. Wharton Jones, 3 by whom they are thus classified. (1.) Constriction 

 may slowly take place, and be slowly succeeded by the normal width ; this is 

 the action of the sulphate of atropia. (2.) Constriction may quickly take 

 place, and be soon succeeded by the normal width, or a width not much exceed- 

 ing the normal ; this is the result of the moderate application of cold, and of 

 mechanical and galvanic irritation. (3.) Constriction either does not take place 

 at all, or when it does, it very rapidly gives place to great dilatation; this is the 

 effect of a weak solution of sulphate of copper, of a strong solution of common 

 salt, of wine, of opium, and of spirit of wine. (4.) Dilatation, preceded or 

 not by momentary constriction, may slowly yield to constriction, which remains 

 permanent ; this is the effect of sulphate of copper, applied in strong solution, 

 or in substance. The electric stimulus is most effectual when applied by the 

 magneto-galvanic apparatus ; and the effects of such application have been espe- 

 cially studied by the Professors Weber. 3 When the minute arteries of the mesen- 

 tery of frogs between 1-7 th and l-17th of a Paris line in diameter, were thus 

 stimulated, they did not immediately respond to the irritation, but began to 

 contract after a few seconds, so that their diameter, in from five to ten seconds, 

 was diminished by a third, and their sectional area consequently reduced to about 

 half ; by a continued application of the stimulus their caliber was so much re- 

 duced that only a single row of corpuscles could pass ; and at last the vessels 

 became completely closed, and the current of blood arrested, the original condi- 

 tions being gradually restored on the cessation of the electric current. Further, 

 it has been ascertained by the careful experiments of Poisseuille (which confirm 

 those of John Hunter) that when an artery is dilated by fluid injected into it, 

 it reacts with a force superior to the distending impulse ; and he has also shown 

 that, if a portion of an artery from an animal recently dead (in which the vital 

 contractility seems to be preserved), and one from an animal that has been dead 



1 See Mr. Paget's "Lectures on Inflammation," in "Medical Gazette," June 7, 1850. 

 As Mr. Paget justly remarks, it is from the mechanical stimulus of the knife that small 

 divided vessels contract and close, so as speedily to cease bleeding ; but this contraction 

 lasts only for a time ; and hemorrhage would commence on their dilatation, if their 

 mouths were not sealed by coagula of blood or lymph. When secondary hemorrhage 

 does occur from want of such coagulation, it is most effectually controlled by the applica- 

 tion of stimuli which, like the actual cautery, induce a more prolonged contraction of the 

 vessels. 



2 "Prize Essay on Inflammation," in " Guy's Hospital Reports" for 1850, pp. 8, 9. 



3 " Muller's Archiv.," 1847. 



