1894.] MICROSCOPICAL JOURNAL. 307 



lows this process, at one time in its passage appearing 

 constricted in the middle, and finally, the leucocyte 

 passes completely through the wall, and moves into the 

 surrounding tissue, by virtue of its amoeboid movements. 



In these four acts, the process, known as the diapedesis 

 of the white blood corpuscles or leucocytes consists, and 

 it is said to be due partly to the independent motility of 

 the leucocytes themselves and partly a filtration of the 

 colloid mass of the cell by the force of the blood pressure, 

 and probably taking place through the spaces between 

 the endothelial cells, the vessel wall itself, having been 

 altered in some way by the process of inflammation. 



In my observations, I very carefully watched all of the 

 phenomena and could observe nothing peculiar during 

 the first stage, i. e. adherence to vessel wall, nor during 

 the passage of the leucocyte through the wall, but in the 

 second stage, i. e. when the cell sends out its process into 

 the wall, I observed a strange thing, namely, that the 

 process sent into the wall by one cell was almost iden- 

 tical with the process that any other cell sent out, both 

 in size and general outline. 



This process was a cone shaped, rather pointed one, 

 which seemed to work its way into the wall of the vessel 

 and, in fact, it seemed to quietly and steadily push its 

 way on and in, until at last it emerged upon the outer 

 side of the vessel. I also noticed in every case, which I 

 observed, where, after adhering, the leucocyte was swept 

 from its hold and carried on in the current, that it re- 

 tained its penetrating process, and did not, as long as I 

 could see it regain its irregularly circular shape. 



From these two facts, it seems more than probable that 

 this penetrating process is due to the activity of the cell 

 itself, rather than that it is such a one as would be pro- 

 duced by the blood pressure acting upon the soft colloid 

 material of the cell and pressing it into the vascular wall, 

 for a process so formed would disappear as soon as the 



