The tanning materials of Europe are of an altogether different type
from those of the United States. The population is so dense that the
quantity of home materials produced is not nearly proportionate to the
amount consumed, and consequently they must draw upon surrounding
lands for their supply. The vegetation of these adjacent countries is
of a much more tropical nature, and it naturally follows that the
tanning materials are also of a different species.
Tanning materials may be divided into two great classes, viz.:
Physiological and pathological.