CIRCULA TION. 



373 



Behavior of the Red Corpuscles. Capillaries will readily be found in 

 which the red corpuscles move two or three abreast, or only in single file. 

 They generally go with their long diameters parallel to, or moderately oblique 

 to, the current. In no case will any blockade of corpuscles occur, so long as 

 the parts are normal. The numerous red corpuscles are seen to be well fitted 

 by their softness and elasticity, as well as by their form and size, for moving 

 through the narrow channels. They bend easily upon themselves as they 

 turn sharp corners, but instantly regain their form when free to do so (see 

 Fig. 96). A very common occurrence is for a corpuscle to catch upon the 

 edge which parts two capillaries at a bifurcation of the network. For some 

 time the corpuscle may remain doubled over the projection like a sack thrown 

 across a horse's back ; but, after oscillating for a while, it will be disengaged, 

 at once return to its own shape, and disappear in one of the two branches 



FIG. 96. To illustrate the behavior of red cor- 

 puscles in the capillaries : the arrows mark the 

 course of the blood : a, a " saddle-bag " corpus- 

 cle; b, a corpuscle bending upon itself as it 

 enters a side branch. 



FIG. 97. To illustrate the deformity pro- 

 duced in red corpuscles in passing through 

 a capillary of a less diameter than them- 

 selves. 



(see Fig. 96). It is instructive to watch red corpuscles passing in single file 

 through a capillary the calibre of which, at the time, is actually less than the 

 shorter diameter of the corpuscles. Through such a capillary each corpuscle 

 is squeezed, with lengthening and narrowing of its soft mass, but on emerging 

 into a larger vessel its elasticity at once corrects even this deformity ; it regains 

 its form, and passes on (Fig. 97). 



Evidences of Friction. In the minute vessels, capillary and other, cer- 

 tain appearances should carefully be observed which are the direct ocular 

 evidence of that friction which we shall find to be one of the prime forces 

 concerned in the blood-movement, to which it constitutes a strong resistance. 

 If, in a channel which admits three red corpuscles beside one another, three 

 be observed when just abreast, it will be found that very soon the middle one 

 forges ahead, indicating that the stream is swiftest at its core. This is because 

 the friction within the vessel is least in the middle, and progressively greater 

 outward to the wall (Fig. 98). In the small veins the signs of friction are 



