CHAP, iv.] THE VASCULAR MECHANISM. 337 



usual, and even in the arteries these are abundant, though not 

 forming the distinct layer seen in the veins. The white? cor- 

 puscles however are not the only bodies present in the peri- 

 pheral zone. Though in the normal circulation blood-platelets 

 (see 33) cannot be seen in the peripheral zone, and hence must 

 be confined (on the view, which has the greater support, that 

 these bodies are really present in quite normal blood) to the axial 

 stream, they make their appearance in that zone with the changes 

 which we are now describing. Indeed in many cases they are far 

 more abundant than the white corpuscles, the latter appearing 

 imbedded at intervals in masses of the former. Soon after their 

 appearance the individual platelets lose their outline and run 

 together into formless masses. 



183. This much, the appearance of numerous white cor- 

 puscles and platelets in the peripheral zones, may take place while 

 the stream, though less rapid than at the very first, still remains 

 rapid ; so rapid at all events that, owing to the increased width 

 of the passages, in spite of the obstruction offered by the adherent 

 white corpuscles, the total quantity of blood flowing in a given 

 time through the inflamed area is greater than normal. But 

 soon, though the vessels still remain dilated, the stream is observed 

 most distinctly to slacken and then a remarkable phenomenon 

 makes its appearance. The white corpuscles lying in contact with 

 the walls of the veins or of the capillaries are seen to thrust processes 

 through the walls ; and, the process of a corpuscle increasing at the 

 expense of the rest of the body of the corpuscle, the whole cor- 

 puscle, by what appears to be an example of amoeboid movement, 

 makes its way through the wall of the vessel into the lymph 

 space outside ; the perforation appears to take place either in 

 the cement substance joining the epithelioid plates together, or, 

 possibly, by an actual breach through the substance of a plate, 

 the breach being repaired immediately after the passage of the 

 corpuscle. This is the migration of the white corpuscles to which 

 we alluded in 32, and takes place chiefly in the veins and 

 capillaries, not at all or to a very slight extent in the arteries. 

 Through this migration the lymph spaces around the vessels in 

 the inflamed area become crowded with white corpuscles. At the 

 same time the lymph in the same spaces not only increases in 

 amount but changes somewhat in its chemical characters; it 

 becomes more distinctly and readily coagulable, and is sometimes 

 spoken of as "exudation fluid" or by the older writers as "coagu- 

 lable lymph." This turgescence of the lymph spaces, together 

 with the dilated crowded condition of the blood vessels, gives rise 

 to the swelling which is one of the features of inflammation. 



If the inflammation now passes off the white corpuscles cease to 

 emigrate, cease to stick for any length of time to the sides of the 

 vessels, the stream of blood through the vessels quickens again, and 

 the vessels themselves, though they may remain for a long time 



F. 22 



