vi CIKCULATION OF BLOOD: ITS DISCOVEKY 175 



the peripheral fluid cylinders, being lowest or nil in those imme- 

 diately adhering to the walls of the tube. 



This decrease of velocity of movement from axis to periphery 

 'of the fluid cylinder, as represented by the blood, fully explains the 

 rotation of the leucocytes in the plasmatic layer round an axis 

 perpendicular to the direction of the current. The necessity of 

 this rotation is obvious, when we consider that the leucocytes 

 nearest the axis of the vessels are under the influence of a more 

 rapid current than those nearest the walls. 



The explanation of the fact that the leucocytes are nearly 

 always in contact with the walls of the vessel while the erythro- 

 cytes move along the axial stream, is not (as many think) that 

 some viscosity of their surface makes them adhere to the walls, but 

 lies in the difference between their specific gravity and that of the 

 erythrocytes. It can be demonstrated in the microscope that 

 granules of graphite, carmine, and colophonium suspended in 

 water, and made to circulate in capillary glass tubes, behave like 

 the red and white corpuscles in respect to parietal and axial 

 currents. The granules of graphite, being specifically heavier, swim 

 in the axial current ; the particles of carmine, which are specifically 

 lighter, follow the marginal stream. On the other hand, these last 

 occupy the axial current, when they are made to circulate with 

 grains of colophonium, since the specific gravity of the latter is 

 lower than that of carmine. It has also been determined experi- 

 mentally that the leucocytes leave the parietal current and follow 

 the axial, when they are made to circulate, not with erythrocytes, 

 but with drops of milk, which are specifically lighter (Funke). 



IX. The phenomenon of diapedesis of blood-corpuscles, alluded 

 to in Chap. IV., which may be observed in the microscope, deserves 

 special mention on account of its great importance. 



Cohnheim, in 1867, was the first who directed the attention of 

 biologists to the fact of the active emigration of leucocytes from 

 the blood-stream through the uninjured vessel walls. He founded 

 on this fact a new theory of inflammation and suppuration which 

 is a complete antithesis to that of his celebrated teacher Virchow. 

 The same facts, however, had been observed and described in 1846 

 by Waller, who was the first to recognise the identity of the 

 leucocytes and pus corpuscles, but regarded the migration of the 

 blood-corpuscles as a phenomenon of filtration. 



In 1849 W. Addison formally expressed the concept of an 

 active emigration of the leucocytes, and distinguished various 

 stages in the course of the phenomenon. 



In 1864, v. Eecklinghausen discovered and described the 

 movements of the leucocytes through the spaces of the connective 

 tissue and the lymphatic canaliculi of such tissues as the cornea, 

 which have no blood-vessels, distinguishing between the fixed and 

 the movable or migratory cells. He did not investigate the origin 



