a02 REPORT OF THE HARVARD AFRICAN EXPEDITION 
is hyperkeratosis, much of the thickening of the epidermis being due to serous 
exudate and leucocytic infiltration. In the epidermis, the leucocytes may be 
grouped in circular masses as in miliary abscesses, or scattered profusely through- 
out the epidermis. The elongated papillae are often vascular, infiltrated with 
lymphocytes and leucocytes and show small haemorrhages. The corilum usually 
shows extensive infiltration, particularly in the deeper portions, and in the well- 
developed lesions, plasma cells are very numerous and constitute the great ma- 
jority of the infiltrating cells. In addition there may be small lymphocytes and 

No. 228. — Case 402. Photomicrograph illustrating 
downgrowth of epithelium, infiltration of deeper layers 
of corium, and condition of blood vessels 
an increase in fibroblasts. In many of the cases there is no marked perivascular 
cellular infiltration, which is usually more common in syphilitic lesions. 
We have not (prior to the investigation of the African material obtained 
on this Expedition) studied pathological material obtained from cases with a 
diagnosis of tertiary yaws. So far as we have been able to ascertain, Hallen- 
berger! in the Cameroons alone has compared the tertiary lesions of yaws 
with those of syphilis. He has also referred to the primary lesions. 
In comparing the histological picture of the late lesions of yaws and syphi- 
lis, he points out that in both conditions chronic inflammatory formations 
occur in which there is a tendency to degeneration of the newly-formed tissue, 
and that while each of these diseases possesses these common characteris- 
1 Hallenberger: Beihefte 3, Arch. f. Schiffs-u. Tropen-Hyg. (1916), XX, 5. 
