394 DR, E. KLEIN. 



in the development of the vesicles of the pustule (which in 

 the case of sheep-pox it does not possess) that I think it 

 necessary to compare more closely his assertions with those 

 given in my memoir. 



a. As regards the development. Dr. Unna asserts that 

 in smallpox of man the " Pockenkorper," i.e. the superficial 

 part of rete Malpighii enclosed between the two strata 

 lucida (^in fig. 3) has been part of the stratum lucidum; he 

 assumes that, in consequence of the morbid infection, the 

 middle part of the original stratum lucidum swells up; its 

 cells become again distinct ; their nuclei are visible, and take 

 again to staining, and that this part is now bordered on its 

 lower and upper surface by unchanged stratum lucidum. As 

 the chief reason for this assertion Dr. Unua seems to regard 

 the fact that the ''granular layer," which in the normal 

 condition lies underneath the stratum lucidum, is in the 

 pock-epidermis to be found underneath the lower (or median) 

 stratum lucidum. 



Now, I am not prepared to make any statement regarding 

 the nature of the different parts of the epidermis in small- 

 pox of man ; but as regards smallpox of sheep I can assert 

 that the appearances represented in fig. 3 (see also my first 

 paper on this subject in the ' Philosophical Transactions '), 

 "which in their principal parts entirely correspond to the 

 changes in smallpox of man, as described by Dr. Unna, are 

 produced in the manner described by myself, and not in that 

 stated by this observer, viz. that the superficial layer of the 

 rete Malpighii (d in fig. 3) has become separated from the 

 true rete Malpighii by the new formation of a median stratum 

 lucidum (c). 



That this is so can be proved in (o) an indirect and 

 (/3) direct manner. 



a. It will not, I think, be admitted by any histologist that 

 the horny scales which form the constituent elements of the 

 stratum lucidum are capable of returning into polygonal 

 granular nucleated cells just as little as those of the stratum 

 corneum are capable of such a change. In the case of the 

 primary pustules of sheep-pocks the cells of the upper rete 

 Malpighii (d in fig. 3) are in those parts in which the horni- 

 fication has not proceeded too far, of a distinctly granular 

 substance and possess a well-defined nucleus, which stains 

 with staining fluid, just like that of an ordinary epithelial 

 cell ; in short, they are in all respects identical with the 

 cells of the true rete Malpighii. Double staining with car- 

 mine and hsematoxylin shows one important difference 

 between the two, viz, whereas the true rete Malpighii stains 



