190 



MOVEMENT OF THE BLOOD IN THE VEINS. 



This remarkable phenomenon was described by Waller in 1846. Cohnheim has 



_W recently re-described it, and accord- 



ing to him the out-wandering is a 

 sign of inflammation, and the 

 colourless corpuscles which accum- 

 ulate in the tissues are to be 

 regarded as true pus corpuscles, 

 which may undergo further in- 

 crease by division. 



Stasis. When a strong stim ulus 

 acts on a vascular part, hyper remic 

 redness and swelling occur. Micro- 

 scopic observation shows, that the 

 capillaries and the small vessels 

 are dilated and overfilled with 

 blood -corpuscles ; in some cases a 

 temporary narrowing precedes the 

 dilatation ; simultaneously the 

 velocity of the stream changes: 

 rarely there is a temporary 

 acceleration, more frequently it 

 becomes slower. If the action of 

 the stimulus or irritant be con- 

 tinued, the retardation becomes considerable, the stream moves in jerks, then 

 follows a to and fro movement of the blood-column a sign that stagnation has 

 taken place in other vascular areas. At last, the blood-stream comes completely 

 to a standstill STASIS and the blood-vessels are plugged with blood-corpuscles. 

 .Numerous colourless blood-corpuscles are found in the stationary blood. Whilst 

 these various processes are taking place, the colourless corpuscles more rarely 

 the red pass out of the vessels. Under favourable circumstances the stasis may 

 disappear. The swelling which occurs in the neighbourhood of inflamed parts is 

 chiefly due to the exudation of plasma into the surrounding tissues. [The vapour 

 of chloroform causes hypeneniia of the web (Lister).] 



Fig. 85. 



Small vessel of the mesentery of a frog, show- 

 ing the diapedesis of the colourless 

 corpuscles 0, iv, vascular walls ; a, a, 

 Poiseuille's space ; r, r, red corpuscles ; 

 /, /, colourless corpuscles adhering to 

 the wall, and c, c, in various stages of 

 extrusion ; /, /, extruded corpuscles. 



96. Movement of the Blood in the Veins. 



As already mentioned, in the smallest veins coming from the 

 capillaries, the blood-stream is more rapid than in the capillaries them- 

 selves, but less so than in the corresponding arteries. The stream is 

 uniform, and if no other conditions interfered with it, the venous- 

 stream towards the heart ought to be uniform, but many circumstances 

 affect the stream in different parts of its course. Amongst these are : 

 (1) The relative laxness, great distensibility, and the ready compressibility 

 of the walls, even of the thickest veins. (2) The incomplete filling 

 of the veins, which does not amount to any considerable distension 

 of their walls. (3) The numerous and free anastomoses between 

 adjoining veins, not only between veins lying in the same plane, but 

 also between superficial and deep veins. Hence, if the course of the 

 blood be obstructed in one direction, it readily finds another outlet. 



