270 The Philippine Journal of Science 1923 



Section through the freshly excised nodule shows a smooth, 

 fairly firm, moist, semitranslucent, grayish and yellowish cut 

 surface of greatly thickened epidermis contrasting with the 

 softer, more-pliable corium beneath. There is no crust, only a 

 thin layer of seropurulent exudate on the rather coarsely gran- 

 ular surface. Near the surface are minute reddish purple 

 points, evidently haemorrhages in the epithelium. The gross 

 appearance shows that the yaw is essentially a thickening of 

 the epidermis, in which there is an acute inflammatory exudate 

 but no distinct ulceration. The thickened epidermis measures 

 3 millimeters in width. 



Microscopical examination, — The pieces of tissue fixed in 

 Zenker's fluid were embedded in paraffine in the usual way and 

 thin sections stained with hsematoxylin and eosin, carbol-anilin- 

 fuchsin for bacteria, and by other special methods. 



Microscopically there appears a violent acute inflammation of 

 the epidermis and the immediately underlying corium. One is 

 at once impressed by the greatly elongated papillae of the corium 

 and the deep penetration of corresponding intervening epithelial 

 pegs. The total width of the epidermis is more than twenty 

 times normal. The most acute exudate is within the epidermis 

 and at the apices of papillae. Over the apices of many of those 

 papillae, which extend outward often almost to the surface, and 

 in the surrounding epidermis, there is extensive haemorrhage, 

 the red cells often lying enmeshed in a coarse network of fibrin. 

 Here and there are small pockets of the granular coagulum of 

 serum ; but the most abundant and characteristic component of 

 the exudate is the polymorphonuclear neutrophilic leucocyte. 

 Such leucocytes are present everywhere in enormous numbers 

 throughout the swollen, distorted, and hyperplastic epidermis. 

 They are most numerous in a zone just above the basal layer 

 of epithelium, and least numerous in the deep, thick, epithelial 

 pegs and hair follicles. They occur in the form of discrete or 

 confluent miliary abscesses, rupturing, pushing aside, and dis- 

 solving masses of epithelium. They lie in great numbers dif- 

 fusely scattered throughout wide areas within intercellular 

 spaces between shrunken epithelial cells which are pushed apart 

 by quantities of intercellular fluid, and they wander less con- 

 spicuously, but still in great numbers, between the cells of the 

 less-injured epithelial pegs and hair follicles. They sometimes 

 accumulate in dense groups at the tips of papillae beneath the 

 epithelium, and not infrequently a miliary abscess within the 



