MIGRATION OF THE BLOOD-CORPUSCLES FROM THE VESSELS. l8l 



to the wall; soon they begin to penetrate into the wall and ultimately they make 

 their way completely through it and wander for some distance further into the peri- 

 vascular tissue. It is still a matter of doubt whether the corpuscles force their 

 way through interendothelial stomata, supposed to be present, and then enter 

 the lymphatic vascular system, or whether they simply pass through the cement- 

 substance between the endothelial cells. Several successive steps can be distin- 

 guished in this process of migration, which is known as diapedesis ; (a) adhesion of 

 the leukocytes to the inner surface of the vessel (after gradual retardation in their 

 progress along the wall up to that point) ; (b) extension of processes into and 

 through the vessel-wall; (c) withdrawal of the cell-body, which appears con- 

 stricted at the instant of its passage through the wall of the compression; (d) com- 

 plete passage through the vessel-wall and the further progress of the leukocyte by 

 virtue of its ameboid movement. 



Hering observed that, even under normal conditions, the leukocytes in larger 

 vessels, which are surrounded by lymph-spaces, pass into the lymph-spaces. This 

 observation explains why cells may be found even in such lymph as has not yet 

 passed through any gland. The cause of the migration from the vessels resides, 

 in part, in the independent power of movement on the part of the leukocytes; in 

 part it is a physical phenomenon, namely filtration of the colloid mass of the cell- 

 bodies through the force of the blood-pressure, and in the latter connection, there- 

 fore, essentially dependent upon the intravascular pressure and the velocity of the 

 blood-current. Hering regards the migration of leukocytes and even of a few 

 red blood-cells from the small vessels into the lymphatics as a normal process, 

 which he was able to observe in the mesentery of the frog. The red blood-cells 

 escape from the vessel in the presence of obstruction to the venous flow, which 

 causes, first, escape of blood-plasma through the vessel-wall, and with the 

 plasma the erythrocytes are also forced through, undergoing a marked change of 

 shape on account of the torsion to which they are subjected at the moment when 

 they pass through the vessel-wall, but regaining their shape again after the passage 

 is completed. 



The migration of blood-cells had already been described in 1824 by Dutrochet 

 and in 1846 by Waller; the phenomenon was next more carefully studied by 

 Cohnheim. According to the latter, the migration is a sign of inflammation, and 

 the leukocytes, which accumulate in 

 considerable numbers in the tissue, 

 are to be regarded as true pus-cor- 

 puscles, which may later multiply by 

 division. It should, however, be 

 distinctly stated that, in addition, 

 the connective-tissue cells are also 

 capable, by multiplication, of produc- 

 ing pus-corpuscles, which differ by 

 their greater size from the migrated 

 leukocytes found in pus. 



When a vascular part is sub- 

 jected to severe irritation, hyper- 

 emic reddening and swelling of the 

 part are at once observed. It has 

 been shown by microscopic examina- 

 tion of transparent parts that both 

 the capillaries and the smaller ves- 

 sels become dilated and engorged 

 with blood-cells; sometimes dilata- 

 tion is preceded by a temporary 

 contraction of brief duration. At 

 the same time, a change in the ve- 

 locity of the blood-stream is observed in the vessels. Rarely, and, as a rule, 

 only for a short time, the blood-stream is accelerated; but generally it is retarded. 

 If the irritation be continued, the retardation soon becomes so great that the 

 current only advances intermittently, and a to-and-fro movement of the blood- 

 column is observed, a sign that obstruction has already taken place in peripherally 

 situated vascular areas. Finally, the current in the distended vessels comes to a 

 complete standstill (stasis) . Bonders points out the greater number of leukocytes 

 in stagnating blood, and believes correctly that this accumulation of leukocytes 

 is a greater obstacle to their progress, as compared with the erythrocytes. 



FIG. 71. Small Mesenteric Vessel from a Frog Show- 

 ing the Migration of Leukocytes: w w, vessel-wall; 

 a a, Poiseuille's space; r r, red blood-corpuscles; 1 1, 

 leukocytes moving along the wall, at c c in various 

 stages of migration; f f, migrated cells. 



While 



