MINUTE ANATOMY OF EPIDERMIS IN SMALLPOX OF SHEEP. 397 



general eruption — show that in both cases the formation of the 

 vesicles of the pustule takes place simply in the upper and 

 middle cell-layers of the rete Malpighii. As regards the 

 vesicles in the pustules of sheep-pox I have shown in my 

 paper in the 'Philosophical Transactions' that hydropic de- 

 generation and vacuolation of the cells of the rete Malpighii 

 plays an important part in their formation. I can now add 

 another fact, noteworthy in considering the modes of their 

 formation. It is this : the intercellular paths (interstitial 

 substance) become widely distended, and by the accumula- 

 tion of fluid (contents of vesicles) gradually transformed in 

 large irregular cavities, the surrounding epithelial cells at the 

 same time becoming compressed and finally disappear. Fig. I, 

 which is a faithful representation of these relations, shows in 

 V vesicles already formed ; i are the intercellular paths, in 

 some places widely distended; through them project the 

 " spikes" of the ridge-and-furrow-cells. In the broad paths 

 (fig. 1) we observe also a thin membranous structure (dark 

 line), and it is not quite clear to me what this means. It 

 possibly means this : during life these broad paths have been 

 filled with a fluid, at any rate a liquefied intercellular sub- 

 stance, which, after death and by the action of the hardening 

 reagent, coagulates ; the coagulum appears in the form of a 

 delicate membrane. At any rate the figure shows that 

 some of the vesicles are derived from distended intercellular 

 paths. 



Dr. Unna's chief reason for maintaining that the vesicles 

 of the pustule are formed in the " Pockenkorper" appears to 

 be the position of the " granular layer." He finds, namely, 

 that at the periphery the " granular layer" may be traced 

 for a little distance underneath the part that contains the 

 vesicles; at all events he does not find the "granular laver" 

 extend above the vesicles. As regards the vesicles in the 

 secondary pustules of sheep-pox — i. e. those of a general 

 eruption — 1 find that there is a considerable difference 

 between the periphery and the centre of the pustule. I have 

 invariably found that in the early stages of the formation of 

 the vesicles these latter are formed underneath the " granular 

 layer/' This is of so constant a character that no error is 

 possible, and we must, therefore, set aside — at any rate for 

 the pustules of sheep-pox of a general eruption — the asser- 

 tion of Dr. Unna that the vesicles are formed above the 

 " granular layer," i. e. within the stratum lucidum. 



In the central part of the pustules of our cases the vesicles 

 are formed in the middle and upper layers of the rete Mal- 

 pighii, as I described and figured in my paper in the ' Phi- 



