308 THE AMERICAN MONTHLY [Oct., 



leucocyte was swept off into the current. Again, the 

 uniformity of tlie shape of the process tends to favor the 

 view tliat the leucocyte penetrates the vessel wall mostly 

 by its own independent power of locomotion. 



Now, as the leucocytes penetrate the vessel in greater 

 and greater numbers, as serum accumulates also, the 

 surrounding tissues become infiltrated and the field ob- 

 served through the microscope becomes covered by a 

 false membrane, composed of leucocytes connective 

 tissue cells, fibrine and serum. 



The above facts constitute the phenomena of inflamma- 

 tion which I observed in the web of the frog's foot. I 

 did not carry my observations further, as I mostly wanted 

 to study the diapedesis of leucocytes, and I found that 

 owing to the amount of material in the field, other than 

 blood vessels, i. e. pigment cells, epithelial cells, etc., I 

 could not obtain a good clear view of the process, and I 

 accordingly conducted all my other observations upon the 

 mesenteries of frogs, and obtained, I believe, a much 

 more accurate view of every step of the process, as far as 

 a microscope will reveal it. 



From the foot-web of the frog then, I observed, be- 

 sides the process usually described, i. e. the adherence to 

 and penetration through the vessel wall, of the leucocyte, 

 two distinct and characteristic phenomena. 



1. The process, which any leucocyte sends into the ves- 

 sel wall in penetrating it, is almost identical, in size and 

 shape, with that which any other leucocyte sends ofl" in 

 the same act, or in other words ; the leucocytes all send 

 off similar processes into the wall of the vessel before 

 penetrating it. 



2. In all the cases which I observed, if a leucocyte, 

 after sending off such a process, is swept from the vessel 

 wall by the current, it always retains that process and 

 does not return to its former shape, providing it had 

 really began penetrating the wall. 



