THE CAPILLARY CIRCULATION. 297 



field by the smaller arteries, shooting through them with great 

 rapidity and in successive impulses, and flowing off again by the 

 veins at a somewhat slow rate. In the capillaries themselves 

 the circulation is considerably less rapid than in either the arteries 

 or the veins. It is also perfectly steady and uninterrupted in its 

 flow. The blood passes along in u uniform and continuous current, 

 without any apparent contraction or dilatation of the vessels, very 



much as if it were flowing 



Fig. 100. 



through glass tubes. An- 

 other very remarkable pe- 

 culiarity of the capillary 

 circulation is that it has no 

 definite direction. The nu 

 merous streams of which it 

 is composed (Fig. 100) do 

 not tend to the right or to 

 the left, nor toward any one 

 particular point. On the 

 contrary, they pass above 

 and below each other, at 

 right angles to each other's 

 course, or even in opposite 



-,. , ^ - , , , CAPILLARY CIRCCLAIIOJJ iu web of f.og's foot. 



directions ; so that the blood, 



while in the capillaries, merely circulates promiscuously among 

 the tissues, in such a manner as to come intimately in contact with 

 every part of their substance. 



The motion of the white and red globules in the circulating blood 

 is also peculiar, and shows very distinctly the difference in their 

 consistency and other physical properties. In the larger vessels 

 the red globules are carried along in a dense column, in the central 

 part of the stream; while near the edges of the vessel there is a 

 transparent space occupied only by the clear plasma of the blood, 

 in which no red globules are to be seen. In the smaller vessels, 

 the globules pass along in a narrower column, two by two, or 

 following each other in single file. The flexibility and semi-fluid 

 consistency of these globules are here very apparent, from the 

 readiness with which they become folded up, bent or twisted in 

 turning corners, and the ease with which they glide through minute 

 branches of communication, smaller in diameter than themselves. 

 The white globules, on the other hand, flow more slowl} and with 

 greater difficulty through the vessels. They drag along the exter- 



