MINUTE ANATOMY OF EPIDERMIS IN SMALLPOX OF SHEEP. 395 



of a light purple colour (hseraatoxylin), the upper rete Mal- 

 pighii ((/ iu fig, 3) assumes a pinit colour (carmine), which 

 is deeper in the cells next the strata lucida. As fig. 3 so 

 beautifully shows, this deep pink colour is exhibited not 

 only by cells of the upper rete Malpighii, but also by cells of 

 the true rete Malpighii in the immediate vicinity of the 

 median stratum lucidum, thus showing that those cells of 

 the rete Malpighii which are here becoming converted into 

 parts of the stratum lucidum lie not only in the upper rete 

 Malpighii, but also in the superficial layer of the true rete 

 Malpighii. [As I have described and figured in my paper 

 in the ' Philosophical Transactions,' the median stratum 

 lucidum possesses longer or shorter processes corresponding 

 to the interpapillary processes of the true rete Malpighii ; 

 these are also well shown in the present fig. 3.] 



Those ceils of the rete Malpighii which are being con- 

 verted into part of the stratum lucidum take especially well 

 to carmine staining, as I have convinced myself also in pre- 

 parations of early stages of the pock, e. g. in a stage repre- 

 sented in fig. 2. In this figure the layer d contains those 

 cells; they still show their outlines, although indistinctly, 

 but have lost their nuclei. But what is of paramount im- 

 portance in this figui'e is the fact that the cells of the layer 

 d have almost entirely lost their "granules."" (In all these 

 pathological cases the " granular layer,^' i. e. the layer of cells 

 next the under surface of the stratum lucidum which contain 

 larger or smaller " granules" staining very deeply blue in 

 hsematoxylin, and thus'easily demonstrated, is much broader 

 than in the normal condition. In the present case the layer 

 d has no more distinct granules ; they are to be found in 

 the next lower layer c. Here they are very large spherical or 

 disc-like masses, situated generally at and near the poles of 

 the nucleus of the cell.) And this is in so far of interest, as 

 it shows that the non-presence of granules in d of fig. 3 does 

 not prove that this layer has never been part of the rete 

 Malpighii ; or expressed in a diflPerent way, the presence of 

 granules in cells below the median stratum lucidum of fig. 3 

 does not at all prove that the upper rete {d of fig. 3) has 

 always been part of the stratum lucidum. 



But there is another reason why the upper rete Malpighii 

 of our case {d, fig. 3) has not previously been part of the 

 stratum lucidum, but, on the contrary, has become separated 

 from the deeper rete Malpighii by the appearance of the 

 median stratum lucidum. If we trace the changes of the 

 epidermis from stage to stage we ascertain that the thickness 

 of the (hypertrophied) rete Malpighii is at first greatest in 



