CHAP, iv.] THE VASCULAR MECHANISM. OB 



re-established. The migrated corpuscles move away from the 

 region along the labyrinth of lymph spaces, and the surplus lymph 

 also passes away along the lymph spaces and lymphatic vessels. 



A more powerful action of the irritant may lead to. still other 

 events. More and more white corpuscles, arrested in their passage, 

 .crowd the channels and block the way, so that though the vessels 

 remain dilated, the stream becomes slower and slower, until at last 

 it stops altogether, and ' stagnation ' or ' stasis ' sets in. The red 

 corpuscles are driven in, often in masses, among the white cor- 

 puscles and platelets, the distinction between axial stream and 

 peripheral zone becoming lost ; and arteries, veins and capillaries, 

 all distended, sometimes enormously so, are filled with a mass of 

 mingled red and white corpuscles and platelets. The red corpuscles 

 run together so that their outlines are no longer distinguishable ; 

 they appear to become fused into a homogeneous red mass. And 

 it may now be observed that, not only white corpuscles but also 

 red corpuscles, make their way through the distended and altered 

 walls of the capillaries, chiefly, at all events, at the junctions of 

 the epithelioid plates, into the lymph spaces beyond. This is 

 spoken of as the diapedesis of the red corpuscles. 



This condition of 'stasis' may be the prelude to further 

 mischief, and, indeed, to the death of the tissue, but it, too, like the 

 earlier stage of inflammation, may pass away. As it passes away 

 the outlines of the corpuscles become once more distinct, those on 

 the venous side of the block gradually drop away into the neigh- 

 bouring currents, little by little the whole obstruction is removed, 

 and the current through the area is re-established. 



162. The slowing or the arrest of the blood current described 

 above is not due to any lessening of the heart's beat ; the arterial 

 pulsations, or at least the arterial flow, may be seen to be continued 

 in full force down to the affected area, and there to cease very 

 suddenly. It is not due to the peripheral resistance being 

 increased by any constriction of the small arteries, for these 

 continue dilated, sometimes exceedingly so. It must, therefore, be 

 due to some new and unusual resistance occurring in the area itself, 

 and this we are by many reasons led to attribute to an increased 

 tendency of the corpuscles, especially of the white corpuscles, to 

 stick to the sides of the vessels. The increase of adhesiveness is 

 not caused by any change confined to the corpuscles themselves ; 

 for if after a temporary delay one set of corpuscles has managed to 

 pass away from the affected area, the next set of corpuscles brought 

 to the area in the blood stream is subjected to the same drlay. 

 The cause of the increased adhesiveness must therefore lie in the 

 walls of the blood vessels, or in the tissue of which these form a 

 part. That the increased adhesion is due to the vascular walls and 

 not primarily to the corpuscles themselves is further shewn by the 

 fact that if, in the frog, an artificial blood of normal saline solution, 

 to which milk has been added, be substituted for normal blood, a 



