PUSTULE. 345 



papillae to such an extent, that at these points a layer of such 

 cells extends uninterruptedly to the deepest stratum of the rete 

 Malpighii. This can still be recognised on the sides of the 

 papillas and in the furrows between them, if we make use of the 

 yellowish colour and erect position of its columnar cells as a 

 guide. The state of things over the apices of the papillge is very 

 different. Here we can no longer distinguish any line of 

 demarcation between epithelium and connective tissue ; it is 

 only by dissecting the parts with needles that we find it possible 

 to say : here is the boundary of the papillag ; there begins the 

 cuticle. For my own part I cannot doubt that this is the main 

 source of the young cells which we find in the contents of the 

 vesicle. The irritated papillary body is in a state of the most 

 exuberant proliferation ; the young cells travel towards the 

 surface, where they are set free as embryonic cells and pus- 

 corpuscles before they have time to become developed into 

 epithelia. Some may possibly force their way through between 

 the cells of the rete Malpighii ; the majority migrate outwards 

 from the tips of the papillae where the rete has given way and 

 where the relation between the secreting surface and the 

 secreted products is precisely the same as on a granulating 

 surface. 



The whole process is thus seen to be an acute purulent 

 catarrh of the skin. If we take the preliminary vesicular stao-e 

 into account we may speak of a catarrh originally serous, 

 w^hich has passed into the purulent stage.* Recovery from this 

 state may take place in various ways, according to the treat- 

 ment adopted. If things are left to themselves, a scab is 

 speedily formed by the drying up of the purulent contents of 

 the bleb ; under this scab the formative actions become gradually 

 slower, and end in the production of a new epidermic coat. 

 The scab has been regarded by many as a sort of roof under 

 cover of which nature could proceed undisturbed to the renewal 

 of the epidermis. The hypothesis is as false as it is attractive. 

 The scab is simply a mass of dead and dried organic matter, 



* The word "catarrh" is usually employed to denote the analogous 

 morbid conditions which occur in mucous membranes. Accordingly I 

 shall discuss the special histology of catarrh among the diseases of 

 those membranes. 



