362 
the blood vessels of the lesion, there seems to be no noteworthy change 
affecting them. 
In some lesions a great proportion of the cells in the corium below the 
vesicle present those peculiar changes characterized by the presence of 
eosin-staining nuclear inclusions and direct nuclear division. The cells 
are tranformed to such a degree that it is often impossible to decide to 
what type certain ones belong, but it is evident that nearly all varieties of 
cells are affected including endothelial cells, both in situ upon the vessel 
wall and free in the tissue, connective tissue cells, pigment cells, and 
eosinophiles. The nuclei become swollen, irregular, and lobulated, and 
segment irregularly into smaller nuclei, often of unequal. size. The 
cytoplasm is increased to such an extent that cells of relatively enormous 
size are produced. When such large cells are of connective tissue origin, 
the cytoplasm presents irregular branching processes. Occluded blood 
vessels were found in several instances. The occlusion was due to the 
presence of large multinucleated cells within the vessel. In another 
instance a group of large multinucleated cells extended through sixteen 
sections (eighty micromillimeters) of the tissue in close relation to a 
blood vessel. It would seem that large multinucleated cells occasionally 
develop from the endothelium of the blood vessels and lymphatics involved 
in the lesion. 
Later in the process phagocytosis becomes a prominent feature. The 
endothelial cells are found in varying numbers in the cavity of the vesicle 
where they are engaged in devouring the remains of epithelial cells. 
That portion of the corium which forms the floor of the vesicle is 
infiltrated with these phagocytic endothelial cells. Phagocytosis is found 
in a greater or less degree throughout the corium of the lesion. At this 
stage small numbers of polymorphonuclear leucocytes are present in the 
corium. On the other hand, if bacteria have gained entrance, poly- 
morphonuclear leucocytes are found infiltrating the tissues in great 
numbers. Their appearance seems to be of the nature of a secondary 
phenomenon rather than an essential part of the process. 
In the majority of lesions the active process ends soon after the destruc- 
tion of the involved portion of the epidermis is completed. Many of the 
resulting necrotic epithelial cells appear either as dense hyaline or as 
faintly stained masses both free in the exudate and along the floor of 
the vesicle. Phagocytic cells are present in varying numbers but there is 
usually a large number present in the cavity of vesicles of four days 
duration. In the uncomplicated process, polynuclear leucocytes are 
relatively rare even in the older vesicles. When the destructive process 
is at an end, the demarcation between the living and the necrotic epi- 
thelium becomes distinct. 'The former grows inward over the floor of 
the vesicle, following the surface of the papille. This rapidly growing 
epidermis presents the same characteristics as that growing over any 
defect. The absence of pigment in the newly formed epidermis accounts 
