390 DR. E. KLEIN. 



the central part of the pock, and, as T described in ray paper 

 ('Philosophical Transactions'), abruptly passes into the epi- 

 dermis of the surrounding skin. But when the median 

 horny streak (median stratum lucidum) has made its appear- 

 ance in the centre of the pock — (as a rule it first appears in the 

 centre of the pock, and gradually spreads from here towards 

 the periphery, as I fully described in the * Philosophi- 

 cal Transactions') — the rete Malpighii of the periphery, 

 where there is no median horny streak, greatly exceeds in 

 thickness the deep rete Malpighii of the centre; it exceeds 

 in thickness even both the deep and upper rete Malpighii 

 taken together. The explanation is not difficult to find ; 

 it is this : upper rete Malpighii, median horny streak and 

 deep rete Malpighii (fig. 3) together once formed a uniform 

 rete Malpighii in the centre of the pock ; its thickness was 

 then, of course, much greater than now, when by the horni- 

 fication of some layers of cells (median horny streak) so 

 much of its thickness has been lost. 



/3. The more direct proof that the upper rete Malpighii 

 {d, fig. 3) has never been part of the original stratum 

 lucidum is to be found in the fact that the median horny 

 streak (median stratum lucidum) may be said to develop out 

 of isolated horny masses of epithelial cells, which gradually 

 become confluent, as I minutely described and figured in my 

 paper in the ' Philosophical Transactions.' 



The fact that " granular cells" {b of fig. 3) are found 

 underneath the median horny streak does not prove that 

 this latter is part of the original stratum lucidum — (in tiie 

 normal epidermis the '' granular cells" lie in close contact 

 with the stratum lucidum, and one may be taken as index of 

 the other) — for I have shown above (see fig. 2) that in our 

 cases the position of the " granular cells" is not invariably 

 a fixed one. 



As I have pointed out in my paper in the ' Philosophical 

 Transactions ' the above condition, viz. appearance of a median 

 horny streak is to be found in the primary pustules only, 

 i.e. in those which appear directly at the seat of inoculation, 

 and this condition does not precede the formation of the 

 vesicles, as Dr. Unna maintains for the smallpox in man. 



Dr. Unna attributes to the " Pockenkorper'' a great 

 importance, inasmuch as he regards it as the seat of the 

 vesicles of the pustule in human smallpox. A comparison of 

 his figures (1. c, Plate XV, figs. 3 and 4) with those which I 

 obtained from secondary pustules of sheep-pocks — i.e. those 

 that appeared like smallpox in man, in consequence of a 



