8 



INFLAMMATION. 



the case, for, as Paget observes, " As the vessels are contracting, 

 the blood flows in them more slowly, or begins to oscillate ; nay, 

 sometimes, I think, even before the vessels begin visibly to 

 contract, one may observe that the blood moves more slowly 

 in them, as if this were an earlier effect of the stimulus ; nor 

 have I seen (what has been commonly described) the acceleration 

 of the flow of blood in the contracting vessels." He again 

 remarks — " It has been commonly said, that as the vessels con- 

 tract, therefore the movement of blood becomes more rapid in 

 them, as when a river entering a narrow course moves through 

 it with a faster stream, and that then, as the vessels widen, so 

 the stream becomes in the same proportion slower. But this 

 is far from true ; the stream becomes slower as the artery or 

 vein becomes narrowed by contraction, and then, as the tube 

 dilates, the stream grows faster, and then, without any appreci- 

 able change of size, it may become slower again, till complete 

 stagnation ensues in, at least, some part of the blood-vessels." 

 Now, the reader must remember that arteries are supplied with 

 muscular or contractile power, and when they are acted upon by 

 any influence which causes a contraction of their muscular coat, 

 they must, of course, become narrower, inasmuch as the muscular 

 cells lie in rings around them. The consequence then is, that 

 less blood penetrates the part of the body supplied by such 

 arteries. The more muscular an artery is, the more lasting and 



Fig. 2. — Irregular contraction of small vessels in the web of a frog's foot after 

 the appHcation of stimuU. — (Wharton Jones.) 



forcible is the contraction, and the greater the obstruction ex- 



