DK. E. KLEIN ON THE SMALLPOX OF SHEEP. 
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incorporated. By the gradual coalescence of groups of vesicles, smaller or larger 
spherical, irregular, or elongated sinuses are formed, which may acquire a large size 
by the disappearance of the intervening septa composed of compressed epithelial cells. 
If the formation of the vesicles extends in a horizontal direction and the vesicles are pretty 
close, the epithelial cells subjacent to them form continuous layers of horny scales, 
the nuclei of which soon disappear. And this is the case whatever may be the deve- 
lopment of the horny stratum, and even when it is not distinguishable. The smaller 
vesicles contain clear fluid ; in the larger there are structures, consisting partly of lymph- 
corpuscles but principally of mycelium, which may or may not be in fructification. I 
have preparations in which spores of exactly the kind described in the former chapter, 
and represented in Plate 32. fig. 11 and Plate 31. fig. 10, V., could be very distinctly 
traced from the papillae through the deeper strata of the rete Malpighii into the vesicles. 
In some cavities the mycelium is dense and composed of filaments so thin that it 
looks like a zoogloea, especially where the filaments are beset with very small conidia. 
In such cavities the fructification of the mycelium is probably going on with very great 
rapidity and intensity (Plate 29. fig. 18 and Plate 30. fig. 19). In those cavities which 
lie deepest, that is, most remote from the layer which is the seat of the horny trans- 
formation of the rete Malpighii, it can be made out, by the examination of different 
cavities lying side by side, that by fructification the mycelium may assume an appear- 
ance similar to that of zoogloea of Micrococci. The comparison of the two conditions 
can even be made in one and the same cavity, which may contain in one part very 
distinct mycelium with conidia, in another material like zoogloea — the transition from 
the former to the latter consisting in this, that the filaments of the mycelium gradually 
become thinner and their network denser, while the spores diminish in size by division 
and are more closely aggregated. 
The infiltration of the vesicular cavities with lymph-corpuscles from the papillae takes 
place in some cases simultaneously with this formation, sometimes later. It commences 
at the periphery of the pock, where the subjacent tissue is most intensely infiltrated, 
and spreads from thence towards the centre (cf. Plate 32. figs. 14 & 15). Besides the 
lymph-corpuscles migrating through the deep stratum of the rete Malpighii, there are 
seen also other small highly refractive bodies which, from their aspect, I am inclined 
to take as spores. 
Many of the lymph-corpuscles themselves contain a number of spherical bodies which, 
from their characters, cannot easily be assumed to be their nuclei, being of a greenish 
colour, and being similar to those found free beside the lymph-corpuscles on their way 
through the deep stratum of the rete Malpighii and in the papillary tissue; they 
correspond probably also to spores. 
This is in accordance with what was found in the pus-corpuscles of fresh lymph (see 
Plate 31. fig. 10, III., and Plate 29. fig. 3, i). I can easily imagine that lymph- 
corpuscles, while migrating from the papillary tissue into the rete Malpighii, take up 
the spores lying in the former and carry them with them just as they would take up 
