44 PRINCIPLES OF VETERINARY SURGERY 



we may have all the vascular changes in an acute inflanima- 

 tion without the intervention of the nervous system. When 

 the irritant is sufficiently toxic to affect the blood-vessels, a 

 momentary spasm of the vessels is noted, together with an 

 acceleration of the blood current. This is immediately fol- 

 lowed by a dilatation of the capillaries and arterioles accom- 

 panied by a marked retardation of the current of blood. In 

 severe inflammations, degenerations occur in the wall of the 

 blood-vessels which increase their porosity. The endothelial 

 cells lining the blood-vessels and lymphatics are not only 

 contractile, but according to Metchnikoff, are phagocytic 

 and mobile. As the current of blood slows down, the cor- 

 puscles pass into the periphery of the stream and the axial 

 character of the current is lost. Normally the corpuscles are 

 carried in the central current of the circulating blood, while 

 the marginal zone consists wholly of plasma. As the leucor 

 cytes reach the periphery of the vessel, they attach them- 

 selves to its wall and finally force their way through it. This 

 is emigration, designated by some authors, diapedesis and 

 transmigration. Diapedesis, however, is a term usually ap- 

 plied to the red blood corpuscles. The leucocytes represent 

 an active process on account of their ameboid movement. 

 The red blood cells which have collected to form dense 

 masses also escape through the vessel wall, being passively 

 forced through by increased pressure. They generally suc- 

 ceed the passage of the leucocytes except in those cases 

 where there is a severe injury to the vessels, thu's causing a 

 hemorrhage. A small amount of serous fluid usually escapes 

 at the same time. 



EMIGRATION. — Normally, a few leucocytes are con- 

 tinually passing from the capillaries into the tissues ; they are 

 wandering cells of the body; but in inflammation, their emi- 

 gration is increased very markedly when the irritant consists 

 of pyogenic bacteria, and slightly in such cases as tetanus. 



