306 THE AMERICAN MONTHLY [Oct,, 



vessel wall, or else the vessel became so thickly packed 

 with corpuscles as to present the appearance of a red in- 

 jection mass, all movement ceasing. The contents of the 

 vessel sways forward and backward with the impulse 

 transmitted to the stream by the beating- of the heart. 

 This is known as the stage of oscillation and is succeeded 

 by a complete stagnation, called stasis, in which no move- 

 ment of any kind occurs. 



I have spoken of the accumulation of leucocytes along 

 the vessel wall, as though in this last instance it did not 

 occur ; by this, I mean that in my observations the vessel 

 filled so rapidly that the accumulation of leucocytes 

 was hidden from view, although if the field thus obscured 

 be watched long enough, the leucocytes are found con- 

 gregating outside the vessel, thus showing that diapedesis 

 still goes on. 



When, however, the blood stream still continues to 

 move on, the leucocytes accumulate more and more, until 

 the vessel wall in some cases, becomes lined with them, 

 often two or three cells in thickness. 



If such a small vein be watched very carefully for a 

 varying space of time, from half an hour to several hours, 

 the following phenomena are seen to take place. (It is 

 not necessary, however, that the vessel wall be lined with 

 leucocytes in order that these phenomena take place, for 

 in all those observations in which I obtained the clearest 

 and best view of the process, the leucocytes were only 

 situated here and there upon the vessel wall.) 



As the vessel is watched, the leucocytes are seen to 

 gradually penetrate its wall, and finally to emerge upon 

 the other side, having passed entirely through the vessel 

 wall into the surrounding tissues. 



This process seems to be divided into four distinct acts. 

 At first the leucocyte is seen to adhere to the vessel wall; 

 then it sends a process into and through the wall; follow- 

 ing this, the remainder of the cell is drawn after or fol- 



