The Production of Skin Carcinoma in the White Rat by Ordinary Gas-Works Tar

Abstract

Introduction The rat is extremely resistant to tarring. The following résumé of the literature is taken chiefly from Watson9s account (1). All early attempts to produce epithelial carcinoma by simple tarring failed. Herly (2), using a tar diluted 50 per cent with glycerol, and containing 1 per cent of arsenious acid, tarred rats for 226 days, then suspended tarring for five months, and at the end of that period resumed tarring of the 16 survivors on the 381st day, continuing it until the 444th day. On the 511th day one rat had a cutaneous horn, which was proved to be a carcinoma. Watson (1) found that preliminary treatment of depilated areas with ether extract of rat tissue favoured carcinogenic response. He believes that the lipoid merely facilitates absorption of the tar (1), and the same effect may be attributed to the glycerol in Herly9s experiments. Dentici (3) found a papilloma in one of 30 rats after 176 days9 treatment. Cholewa (4) repeatedly cauterized the depilated area for seven months, then tarred for five months, and got a wart in one animal, which he believed to be a squamous-cell epithelioma. Some success has been obtained with other carcinogenic agents. Guilera, Roca and Corachan (5), using a commercial preparation of mineral tar, for which no details are given, painted 40 rats three times a week and obtained one carcinoma at the end of three months. Watson (6), using pinene tar, a pure turpentine tar which had been shown by tests on mice to be more carcinogenic than gas-works tar, was able to produce tumors in rats after preliminary treatment with ether extracts. Without such preliminary treatment his results were as follows. After seven months9 tarring with pinene tar only, followed by three months9 rest, he obtained on the 296th day a papilloma in one rat, which died about the 400th day without development of malignancy, and on the 345th day a squamous-cell carcinoma in another animal, which was still alive on the 600th day from commencement of tarring. He remarks: “The malignant tumour produced without the use of the lipoid extract is apparently the first recorded case in the literature of a skin tumour in the rat produced by means of tar alone.”