THE CAPILLAR Y CIRCULATION. 113 



the veins. On account of the reticular arrangement of the capillaries, 

 the direction of the stream through them is by no means constant ; 

 for a period there may be a complete cessation of the How in a capillary 

 channel, or the direction of the current may even be reversed for a longer 

 or shorter time. The now through the arteries is by far the most 

 rapid. In the veins also the stream is so rapid that it is difficult to 

 catch the contour of the corpuscles. The stream is slower in the small 

 veins, and in the capillaries the movement is, as a rule, so tardy 

 that the individual corpuscles can be followed without any difficulty. 

 The inconstancy of the capillary stream is generally apparent. If a 

 group of capillaries be kept for some time under observation, the blood 

 is occasionally seen to hurry suddenly through a number of these with 

 increased rapidity ; this continues for a while, and then the stream becomes 

 again slower and slower, till after an interval it reassumes the usual 

 quiet rate of flow which has been maintained without interruption in 

 the neighbouring capillaries. These variations depend on alterations in 

 the lumen of the afferent arteries. 1 



The arterial stream is pulsatile, and each systole may be recognised 

 even in very small arteries by the rhythmical acceleration and retardation 

 of the blood stream. Such a rhythmical movement is absent from the 

 capillaries and veins in a normal condition ; the stream is a continuous 

 one in both. In the arteries the mass of red corpuscles does not com- 

 pletely occupy the lumen, but moves along the axis of the stream. To 

 the outside there lies a clear layer of plasma, in which here and there a 

 stray white corpuscle rolls along. In the veins there is also a similar 

 peripheral plasmatic layer, in which the white corpuscles roll slowly 

 along, sticking now and again to the wall of the vessels in their course. 

 In the smallest capillaries the plasma layer cannot be distinguished, the 

 red corpuscles march in single file, and often become distorted and bent 

 as they pass. These capillaries are invisible if by any chance the file 

 of corpuscles ceases to pass through them. Thus in the course of an 

 observation capillaries may be seen to appear and vanish from view. 

 In the angles of the capillary network, red corpuscles may sometimes 

 be seen to stick and hang in the balance, bent round the angle, half in 

 one branch and half in another, until finally swept on into the rush and 

 hurry of the stream. 



The white corpuscles progress with a slow rolling motion in the 

 plasmatic layer. The axial stream travels with the greater velocity, 

 and thus the side of the leucocyte which at any moment lies nearer the 

 axis is driven on with the greater speed ; hence the rolling .movement. 

 The white corpuscles travel in the peripheral layer, the red in the axial 

 layer, for the latter are the heavier. It is not, as has been supposed, 

 that the white are lighter and the red corpuscles heavier than the 

 plasma ; both forms are of a higher density than the plasma. 



Schklarewsky 2 found that, when he circulated particles of graphite 

 and carmine through glass capillaries, the carmine travelled in the peri- 

 pheral layer. When he substituted resin in the place of graphite, the 

 carmine travelled in the axis. When he circulated pus corpuscles and 

 milk globules, the pus corpuscles occupied the axial stream. 



The capillary circulation no longer remains pulseless, if the resistance 



1 Cohnhehn, "Lectures on General Pathology," New Syd. Soc. Translation, 1889, 

 vol. i. pp. 152, 153. 



2 Arch.f. d. ges. PhysioL, Bonn, 1868, Bd. i. S. 603. 



VOL. II. 8 



