Abstract
Recent and older careful studies of cancer have shown that this disease may be induced by a variety of substances and conditions; such as coal tar, various lipoid solvents, arsenic, various animal parasites, X-ray, radium, etc. In mice it occurs most frequently in certain families (Maude Slye). In man it may arise in certain congenital defects and tumors and in old inflammatory processes. 1
These same studies have further indicated that cancer unlike the inflammatory processes when once induced is not dependent any longer upon these original exciting agents. Cancers once induced by coal tar may be transplanted through many generations of animals. 2
From observations cited in the three preceding papers of this series it is evident that an independent growth of body cells is dependent on a crowding of these cells together and a relative decrease in their blood supply. It became thus of interest to see what might be the nature of the changes induced by these various excitants of cancer. This work was just begun three years ago. It has been described in part in other papers.
Ross 3 in discussing the action of these various substances which lead to cancer thought them direct excitants of cell division. It seemed evident to me from my studies of the factors regulating cellular growth in the organism that their action might be otherwise. Fischer1 many years ago had already shown that when drops of olive oil containing Sharlach R are introduced just beneath the epidermis the epithelial cells are attracted to these drops. These cells surround the drops of oil to form dense cell masses not unlike those of cancer. Jorstad 4 working in my laboratory has found that coal tar acts in the same manner.
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