T H E C A P I L L A K I E S. 139 



rent, begiii_t0 crowd in numbers against the vascular wall, as 

 was long ago described by Dr. Williams. In this way the 

 vein becomes lined with a continuous pavement of these bodies, 

 which remain almost motionless, notwithstanding that the 

 axial current sweeps by them as continuously as before, though 

 with abated velocity. Now is the moment at which the eye 

 must be fixed on the outer contour of the vessel, from which 

 (to quote Professor Cohnheim's words) here and there minute, 

 colorless, button-shaped elevations spring, just as if they were 

 produced by budding out of the wall of the vessel itself. The 

 buds increase gradually and slowly in size, until each assumes 

 the form of a hemispherical projection, of width corresponding 

 to that of a leucocyte. Eventually the hemisphere is convert- 

 ed into a pear-shaped body, the small end of which is still at- 

 tached to the surface of the vein, while the round part pro- 

 jects freely. Gradually the little mass of protoplasm removes 

 itself further and further away, and, as it does so, begins to 

 shoot out delicate prongs of transparent protoplasm from its 

 surface, in nowise differing in their aspect from the slender 

 thread by which it is still moored to the vessel. Finally the 

 thread is severed, and the process is complete. The observer 

 has before him an emigrant leucocyte, which in all apprecia- 

 ble respects resembles those which have been already de- 

 scribed in the aqueous humor of the inflamed eye." 



Various explanations of these remarkable phenomena have 

 been suggested. Probably the nearest to the truth are those 

 which attribute the chief share in the process to the vital en- 

 dowments with respect to mobility and contractility of the 

 parts concerned both of the corpuscles (Bastian) and the cap- 

 illary wall (Strieker). Dr. Sanderson remarks, " The capillary 

 is not a dead conduit, but a tube of living protoplasm. There 

 is no difficulty in understanding how the membrane may open 

 to allow the escape of leucocytes, and close again after they 

 have passed out ; for it is one of the most striking peculiari- 

 ties of contractile substance that when two parts of the same 

 mass are separated, and again brought into contact, they melt 

 together as if they had not been severed." 



Hitherto, the escape of the corpuscles from the interior of 

 the bloodvessels into the surrounding tissues has been studied 

 chiefly in connection with pathology. But it is impossible to 

 say, at present, to what degree the discovery may not influence 

 all present notions regarding the nutrition of the tissues, even 

 in health. 



The circulation through the capillaries must, of necessity, 

 be largely influenced by that which occurs in the vessels on 

 either side of them in the arteries or the veins ; their in- 



