YAWS AND SYPHILIS 299 
blood vessels of the corium. The organism lies particularly in the connective 
tissue in the lymph spaces between the cells and various fibrils, in the adventitia 
and more rarely in the intima of the blood vessels. The inflammatory reaction 
which results consists particularly of plasma cells, endothelial and polymor- 
phonuclear leucocytes, occasionally eosinophils and fibroblasts. Mitosis of the 
= 
© e 
, 
« & 

No. 223. — Case 403. Photomicrograph of small vessels with endothelial proliferation 
and infiltration of the corium 
endothelial leucocytes, fibroblasts, and lymphocytes is common. The epidermis 
often shows infiltration with leucocytes and plasma cells. In the corium the 
infiltration is especially perivascular, in the papillae, and also interstitial. 
A striking feature often observed is the accumulation of large numbers of 
endothelial cells about the blood vessels and lymphocytes, the walls of the 
blood vessels being sometimes filled with cells. Such a picture is especially 
observed about the arteries when the smooth muscle cells have undergone ne- 
crosis and the internal layer has become greatly thickened. 
Regeneration in the corium takes place both around and between the blood 
vessels with infiltrations of endothelial leucocytes, lymphocytes, polymorphonu- 
clear leucocytes and particularly proliferating fibroblasts. Such a process also 
