240 DR, KLEIN. 
represents a vertical section through the central portion of a 
primary pock on the eighth day. 
The stratum corneum is unaltered. The newly formed 
horny layer by which the rete Malpighii is abnormally split 
into a superficial and a deep layer, is seen to be formed by 
the transformation of the cells which lie next to it on its 
superficial aspect. On its deep surface are cells which are 
much enlarged and contain vacuoles ; they present the ap- 
pearance to which pathological histologists frequently apply 
the term dropsical. It is by the subsequent dilatation of 
these enlarged cells that the vesicular cavities (“ cell” of the 
older authors) are formed ; between them the septa are seen 
composed of flattened and scaly cells which, as above de- 
scribed, extend from the horny layer towards the interpa- 
pillary processes. The drawing further shows the remarkable 
changes which take place in the papillary processes them- 
selves simultaneously with the formation of the horny layer. 
In consequence of the very active germination of the cells of 
which these processes consist, they send down conical or 
cylindrical sprouts into the corium; it sometimes happens 
that the end of one of these sprouts is cut off, so that it 
presents itself in the section as an island of cells (2) sur- 
rounded by the tissue of the corium. 
7. The vesicles, once formed, increase in size and number. 
Originally separate, and containing only clear liquid, they 
coalesce, as they get larger, into irregular sinuses, and are 
then seen to contain masses of vegetation similar to those 
which have been already described in the lymphatic system 
of the corium—with this difference, that the filaments of 
which the masses are composed are of such extreme tenuity, 
and the conidia are so small and numerous, that the whole 
possesses the characters of zooglea rather than of mycelium. 
There appears to me to be little doubt that these aggrega- 
tions are produced in the same way as the others, viz., by 
the detachment of conidia from the ends of filaments. The 
characters of the vegetation contained in the vesicular cavities 
are well shown in fig. 10. The contents of a single vesicle, 
as seen under a much higher power, are represented in 
fig. 11. In the earlier stages of the process the cavities con- 
tain scarcely any young cells. Sooner or later, however, so 
much of the rete Malpighii as lies between the horny stratum 
and the papille becomes infiltrated with migratory lymph- 
corpuscles. The process can be plainly traced in the sections. 
At the period of vesiculation, z.e. at a time corresponding to 
layer of do., (¢) newly formed horny layer, (e) superficial or papillary layer 
of corium. 
