244 
DR. E. KLEIN ON THE SMALLPOX OE SHEEP. 
another point, as regards the distribution of the vesicles, which I think important, viz. 
that even in those pocks in which there was a very marked central depression, the most 
numerous and best developed vesicles were found in the centre, and they became smaller 
and fewer the nearer to the periphery — thus showing clearly that the depression in the 
centre is n'ot caused by the disappearance of previously existing vesicles. 
I have now to call the attention of the reader to Plate 29. fig. 16, in which the 
formation of the vesicles is shown, as well as the presence of an Oidium- like fungus in 
their contents. 
In some vesicles the mycelium, which here also is composed of filaments of very 
various thickness, is imbedded in a finely granular matrix, which I suppose is only 
coagulated plasma ; in others the matrix is almost homogeneous, and is stained slightly 
with carmine and hsematoxylin as in D. After some time pus-corpuscles are seen to 
penetrate from the papillary tissue through the deeper strata of the rete Malpighii into 
the vesicles, just as in the primary pocks. So also the transformation of the mycelium 
in the vesicles by rapid fructification into a zooglcea-like mass of Micrococcus occurs in 
the manner already described. I have represented the characters of the mycelium and 
the spores attached to it in Plate 29. fig. 17, drawn with every possible accuracy 
from the contents of a vesicle of a secondary pock. 
The mycelium, as well as the spores, possess a greenish colour, and are of a bright 
and shining aspect. 
As peculiarities which I had not seen in any of the primary pocks, and in only one 
secondary pock of the upper and one of the lower lip, may be mentioned the occurrence 
of blood in a single vesicular cavity, the rest not containing any. This vesicle was 
situated rather deeply in the rete Malpighii. In another instance I observed the 
effusion of blood into the sheath of a hair-follicle and into the adventitia of an artery. 
In both'cases the blood was contained in a number of large irregular spaces communi- 
cating with each other. 
I am unable to refer the fungus of which we have spoken in the foregoing and in 
this chapter, and which, as we have mentioned and figured, occurs first in the tissue of 
the corium and its lymphatics and is gradually carried or penetrates into the vesicles 
formed in the rete Malpighii, to any described species, and would propose to call it 
provisionally Oidium variolce. 
Although nobody could, from the very great distribution of this fungus through the 
whole pock, take it to be a mere accidental entophyte, yet it might be objected that we 
are wrong in asserting that its development begins and ends in Micrococcus. Against 
this objection it must be maintained that, besides our being able to follow the one into 
the other as far as place as well as time is concerned, we also find (and this appears to 
me to be of still greater importance) at one time only the one organism and at another 
time only the other ; we have found first only the Micrococcus , then we have found 
only the Oidium form, which we finally see again replaced by Micrococcus. Whether 
a form of vegetation corresponding to Oidium variolce in sheep is to be met with in 
