Frederic E. Mohs, MD, and the history of zinc chloride.

The history of zinc chloride therapy before and including Frederic E. Mohs' (1910-2002) early contributions to dermatologic oncology is presented. In 1932, Mohs devised a method of cutaneous surgery that employed zinc-chloride paste to devitalize basal or squamous cell carcinoma. Because zinc chloride coagulates malignant tissue without destroying cellular architecture, he described the surgery and its preservative effect as the fixed-tissue method. This method involved the serial removal of devitalized malignant tissue and the freezing and histologic examination of each layer; the process was continued until a cancer-free plane was reached. In 1953, a modified version of the micrographic system, the fresh-tissue method, was introduced. For improved efficiency, Mohs retained the systematic mapping of a neoplasm but eliminated the chemical escharotic. Although the fresh-tissue method has become the preferred treatment mode, zinc-chloride paste therapy remains in use today. Although the history of Mohs micrographic surgery is well documented, its background has not received sufficient attention. This paper surveys the chemical synthesis of zinc chloride, the formulation of zinc-chloride paste as a cutaneous escharotic, and the extent to which Mohs' method compares with those of 19th and early 20th century predecessors.

Long-term changes of acidifying deposition in Finland (1973-2000).

The long-term changes of acidifying deposition in Finland during the period 1973-2000 were studied using bulk deposition data from 19 stations belonging to the national monitoring network. The regional-scale approach (southern, central and northern Finland) was used for trend assessment with respect to implementation of European sulphur (S) emission reduction amendments involving deposition changes prior to (1973-1985) and after (1986-2000) the agreements (S protocols in 1985 and 1994). There were no marked changes in sulphate deposition between the 1970s and 1980s and consistent trends in 1973-1985 were not observed. Deposition of nitrogen (N) compounds, particularly NO3-N, were increasing between the 1970s and 1980s. Deposition of base cations exhibited a slight decline throughout the 1970s and 1980s. Decrease of calcium and magnesium deposition without corresponding decrease in sulphate resulted in increased acidifying potential (AP) of deposition. Due to successful implementation of S (and N) emission reduction measures, sulphate deposition has decreased substantially (30% in northern and up to 60% in southern Finland) since the late 1980s. N deposition also decreased, but less than S deposition. Base cation deposition has also declined substantially, but this decline appeared to be leveling off during the 1990s, accounting for the decrease of AP in deposition. The observed deposition pattern is in agreement with the on-going biochemical recovery of acidified small Finnish lakes taking place since the early 1990s.