398 1)11. E. KLEIN. 



losophical Transactions.' In the periphery, however^ there 

 we certainly meet with appearances which might suggest 

 an interpretation such as is given by Dr. Unna, viz. there we 

 find that the stratum lucidum appears to be separated into 

 two layers, and between these lie the vesicles, generally of a 

 considerable size, and separated only by thin trabecular 

 remains of cell- masses. This condition — i.e. the presence 

 of a median stratum lucidum underneath the vesicles — may 

 be observed at first only at the very periphery ; as develop- 

 ment proceeds it extends also for some distance towards the 

 central part of the pustule. In the very periphery we may 

 find also an indication of a " granular layer" underneath the 

 median stratum lucidum^ traceable into the " granular layer" 

 of the surrounding part. Now_, all this seems to me to admit 

 of an easy and simple interpretation, viz. that in the peri- 

 phery the vesicles become first separated from the subjacent 

 rete Malpighii by the hornification — or whatever that pecu- 

 liar, highly-refractive, homogeneous condition may be — of 

 the cell-layers of the rete Malpighii directly underneath the 

 vesicles. I would particularly draw the attention to fig. 4>, 

 which represents a vertical section through the epidermis of a 

 pustule of a general eruption. The right and middle of the 

 drawing corresponds to the centre, the left to a part near 

 the periphery of the pustule, and it is here seen that in the 

 centre the vesicles lie underneath the '' granular layer," i. e. in 

 the true rete Malpighii; whereas in the periphery the super- 

 ficial vesicles are already becoming separated from the rete 

 Malpighii by a layer, which in its aspect corresponds to the 

 median stratum lucidum. As is also shown in the drawing, 

 it seems to branch off" from the stratum lucidum of the 

 surface. A section placed at a right angle to the plane of 

 that represented in fig. 4 would, if placed through the peri- 

 pheral part, show the vesicles enclosed between two strata 

 lucida, the upper being the true stratum lucidum of the 

 surface, the lower corresponding to the median horny streak 

 (or median stratum lucidum); that is to say, we should find 

 that the vesicles actually correspond in position to the 

 " Pockenkorper," as maintained by Dr. Unna. But if that 

 section were placed through the centre only, we should find 

 no such thing ; we should merely see the vesicles in the 

 middle and upper layers of the true rete Malpighii underneath 

 the " granular layer." 



In an appendix to his paper Dr. Unna mentions that he 

 learned by letter from Dr. Weigert, whose experience in 

 the anatomy of smallpox of man is, I think, universally ad- 

 mitted to be of an authoritative character, that this observer 



