310 THE AMERICAN MONTHLY [Oct., 



Having now thoroughly examined the frog's blood, I 

 turned my attention to the mesentery which was to be 

 my field of operation. This is seen, by the microscope, 

 to be composed of the following elements, being a most 

 typical example of all serous membranes. 



It is transparent, and composed of — 



1. Very fine delicate connective tissue fibrils. 



2. Connective tissue cells. 



3. Some elastic fibres, and it is traversed by a beauti- 

 ful net-work of lymphatic and vascular vessels, and 

 channels. In order to watch for a long time, the process 

 of inflammation in the mesentery, it is necessary to keep 

 it moistened by a weak salt solution (f per cent sol.). 

 Carefully opening the abdomen of the frog and spread- 

 ing the mesentery upon the microscope stage, as de- 

 scribed before, I observed the following phenomena. 



A slight inflammation is caused by simple exposure of 

 the mesentery to the air, and there is a slight dilatation 

 of the arteries with an accelerated current. At this 

 stage we get an appearance as follows : 



The vessels show beautifully lying in the transparent 

 membrane, with no pigment or other matter to obstruct 

 the view. 



The stream of blood is so rapid that it is impossible to 

 distinguish the individual corpuscles, but gradually, the 

 irritation being kept up, in from four to five hours, some- 

 times much sooner, if a medium sized vein be watched, 

 the stream begins to grow slower, and soon the corpus- 

 cles become distinguishable, first in the smaller vessels. 



This slowing occurred sooner in the mesentery than 

 in the web of the foot, and more rapidly the greater the 

 irritation. As the stream becomes slower the same phe- 

 nomena are observed as in the web, namely : the red cor- 

 puscles occupy a central position in the vessel, there be- 

 ing on each side of this stream of red corpuscles, a zone 

 of plasma, in which most, but not all, of the white cor- 



