ELEMENTARY PHYSIOLOGY less, u 



gaps in their succession. Frequently one or more cor- 

 puscles may remain stationary for a moment and tlien 

 pass on again. The red C()r[)uscles, whicli in the froy are 

 oval and comparatively large, glide along with tlieir long 

 axis parallel to the direction of the stream, and may often 

 be observed to be squeezed out of shape by pressure 

 against the wall of the capillary (Fig. 25, G and H). In 

 the larger capillaries, more especially in mammals whose 

 corpuscles are smaller than in the frog, the corpuscles 

 often pass along two or three abreast. Further, in tliese 

 larger capillaries it may be seen that the red corpuscles 

 tend to keep to the centre of the stream, leaving a clear 

 layer of fluid along the sides of the blood-vessels. This 

 is due to the fact that the fluid friction (already referred 

 to on p. 50) is greater close to the walls of the capillaries 

 than in the middle of the stream, and the corpuscles pass 

 along where the resisting friction is least. The colourless 

 or "white" corpuscles usually move more slowly and 

 irregularly than the red, and may, as a rule, be seen to 

 lie in the clearer layer of fluid at the side of the current. 

 Moreover, they frecjuently stoj) for an appreciable time, 

 as if sticking to the wall of the capillary, and then roll on 

 again ; probably because tliey are more adhesive than the 

 red corpuscles as a result of their power of executing 

 anueboid iiioveiuents (see p. 100). 



20. Inflammation. - Everybody is moi-e or less familiar 

 with a i)eculiar and unusual condition whicli may arise in 

 almost any part of the body, and which they describe by 

 speaking of the part as "inflamed." To ordinary obser- 

 vation the characteristics of the condition are that the 

 inflamed region becomes flushed and red, that it feels 

 warmer than usual, that it becomes swelled and painful, 

 and finally, if the inflammation is severe, that a thick 

 yellowish fluid is formed which is commonly known as 

 "matter," or more correctly as pus. Such a .series of 

 changes may be observed during the formation and 

 breaking of a boil. But the several stages just named are 



