l8o MIGRATION OF THE BLOOD-CORPUSCLES FROM THE VESSELS. 



rent becoming accidentally stronger on one side, it is set free, whereupon 

 it rapidly regains its former shape by virtue of its inherent elasticity. 

 When two vessels join to form one, the elasticity of the red blood-cells 

 is again put to proof. Cells at such points are not infrequently heaped 

 up and pushed together in one direction or another. Occasionally, an 

 accumulation of this kind causes a temporary stagnation first in one of 

 the branches and then in the other; the obstruction is then removed, 

 and for some time both capillaries continue to pour their contents into 

 the collecting tube, during which process the corpuscles are shaken up, 

 like dice in a box. 



The movement of the white blood-cells is entirely different. They 

 roll along the walls of the blood-vessels, their peripheral zone bathed by 

 the plasma of Poiseuille's space and their inner spherical surface pro- 

 jecting into the procession of red blood- cells. The explanation of this 

 peculiar property on the part of the leukocytes of keeping close 

 to the vessel-wall has been furnished by Schklarewski, who dem- 

 onstrated by certain physical experiments that in capillary tubes 

 in general (as, for example, glass tubes), containing artificial mixtures 

 of different kinds of granular bodies, those possessing the lowest specific 

 gravity are forced to the wall when a current is set up in the tube, while 

 those having a higher specific gravity move along in the middle of the 

 stream. Thus, when once forced against the wall, the leukocytes must 

 keep on rolling, partly on account of the viscosity of their surface, which 

 causes them to adhere readily to the vessel- wall, and partly because the 

 surface directed toward the axis of the vessel, where the current is 

 swiftest, receives the most effective impulse, often by the direct impact 

 of red corpuscles driven against it. The rolling movement is not rarely 

 intermittent, probably because different parts of the leukocytes adhere 

 with equal tenacity to the vessel- wall. The viscosity of the leukocytes 

 is also in part responsible for their slower movement, which is from ten 

 to twelve times slower than that of the red blood-cells; this is, however, 

 in part also due to the fact that, owing to their parietal position, the larger 

 portion of the body of the leukocyte projects into the peripheral layers 

 of the cylindrical stream, where the current is least rapid. 



It is an interesting observation that in the vessels first formed in the incu- 

 bated egg, as well as in young tadpoles, the movement of the blood from the 

 heart is intermittent. 



The velocity of the stream is influenced also by the diameter of the vessels 

 at a given point. The latter is subject to periodical variations, not only in vessels 

 provided with muscular tissue, but also in the capillaries in the latter in conse- 

 quence of spontaneous contraction of the protoplasmic cells that form their 

 walls. 



In the pulmonary capillaries the blood-stream is more rapid than in those 

 of the greater circulation, whence it may be concluded that the total sectional 

 area of the pulmonary capillaries must be smaller than that of all of the 

 capillaries of the body (of the greater circulation) . 



THE MIGRATION OF THE BLOOD-CORPUSCLES FROM THE 

 VESSELS ; STASIS ; DIAPEDESIS. 



If the circulation be observed in the mesenteric vessels it is not rarely possible, 

 especially if, after the application of a mild irritant to this vascular tissue (the 

 contact of the air alone is sufficient), an inflammatory process begins to develop, 

 to see the migration of leukocytes in varying numbers through the vessel-wall. 

 Instead of rolling along in a jerky manner in the plasmatic zone, the cells gradually 

 move more and more slowly, accumulate in increasing numbers and adhere firmly 



