360 
hyaline and deeply stained with eosin. The hyaline transformation 
makes its first appearance about the nuclei either in the form of a dense 
membrane or as irregular masses. 
The base of the vesicle in which there is an active exudation is almost 
invariably concave. The papille are either totally obliterated or distorted 
through lateral distension. The epithelium in many cases persists 
between these papille for some time after it has been destroyed over the 
more exposed portions. The vesicles are in some instances multilocular 
but the average one is unilocular and stands in marked contrast to . 
the type of lesion found in smallpox. The common involvement of 
hair follicles and sweat ducts in the typical rounded vesicles indicates 
clearly that these structures acting alone do not produce umbilication. 
After the vesicles have become fully formed, other changes occur. To 
the naked eye the vesicles are flaccid and no longer tense, and the fluid ~ 
is clouded. This condition may be seen three or four days after the 
first appearance of the eruption or it may even be present earlier. The 
evaporation and absorption are now more rapid than the out-pouring of 
the exudate. The fluid within the vesicle contains more fibrin than in 
the early stages and phagocytes which are attracted by the dead epithelial 
cells are beginning to appear. The roof of the vesicle, the trabecule, and 
the cells of its lateral wall now take a diffuse stain and are apparently 
dead. The trabeculae are ruptured in almost every instance and their 
remains are to be found projecting downward from the roof of the 
vesicle. The former pressure of exudate has in many instances broken 
peripherally beyond the boundary of the original lesion so that irregular 
spaces are found. The large, rounded epithelial cells lying loose on the 
floor of the vesicle show various degrees of hyaline changes. Some appear 
dense and hyaline, others are stained but faintly. The nucleus is either 
no longer apparent or is represented by irregular, deeply stained masses. 
Probably all the epidermis involved in the lesion is eventually destroyed. 
In some instances a portion of the epithelium which shows none of the 
cell changes that are characteristic of the process, is invaded by numbers 
of phagocytic cells. It is possible that such infiltration of a small focus 
of the epidermis represents the site of a minute process in which the 
initial cells changes have been obscured in the infiltration which has 
followed. The phagocytic cells invade the normal epidermis and are 
found in varying number far from any well defined vesicle. Cause for 
their presence is not to be found in any injury to the epidermis. 
In all the early lesions a pathological process is constantly found in 
the corium. ‘The first change noted is the presence of eosin-staining in- 
clusions situated usually in the nucleus, more rarely in the cytoplasm of 
cells. In what may be considered a very early stage in the process the 
eosin-staining inclusions are limited to the endothelial cells lining the 
small blood vessels. Later, when the process is well advanced, similar 
inclusions occur in a large proportion of the cells in the corium under- 
