The mechanism of carcinogenesis by the neutral fraction of cigarette smoke condensate

Sixteen groups, each of 50 Swiss female SPF mice, were treated thrice weekly with various combinations of 3,4-benzopyrene (BP) and/or the neutral fraction of cigarette smoke (NF) in acetone applied to the skin. Some groups received one carcinogen, some the other and some a mixture of the two. Skin tumour incidence rates were found to increase both with the dose of NF and with the dose of BP. With BP alone a threshold dose was found beyond which a very heavy incidence rate of malignant skin tumours occurred. After correction of the results for intercurrent deaths it was found that when NF and BP are applied together as a mixture they do not act independently in the production of malignant skin tumours but interact positively. This suggests that some of the components of NF act as cocarcinogens rather than as complete carcinogens. Treatment with NF appeared to increase the incidence of malignant lymphomas. The data were not suitable for deciding whether the various treatments influenced the rates of incidence of internal tumours of other types, for example, lung tumours.

Comparative carcinogenicity for mouse-skin of smoke condensates prepared from cigarettes made from the same tobacco cured by two processes

Bright tobacco grown in Mexico was either flue-cured and redried (FC) or air-cured and bulk-fermented (AC). Both FC and AC were made into cigarettes standardized for draw resistance. FC and AC cigarettes were smoked under similar conditions in a smoking machine (one 2-second 25 ml. puff per minute down to a 20 mm. butt length). Condensates were kept at 0-4° C. until applied to the skin of mice.Three groups of 400 female Swiss mice were treated as follows: Group 1- thrice weekly application of 60 mg. FC in 0.25 ml. acetone to the clipped dorsal skin: Group 2- similar treatment with AC; Group 3-thrice weekly application of 0.25 ml. acetone only.Chemical analysis of the 2 tobaccos and 2 condensates revealed only small differences in composition and it is noteworthy that the concentration of reducing sugars was almost as high as in the AC tobacco as in the FC tobacco.The risk of development of skin tumours, particularly malignant skin tumours, was higher in FC-treated mice than in AC-treated mice (p < 0.01), but the difference may have been due to the use of equal weights of condensates rather than the use of extracts from equal numbers of cigarettes, since the AC cigarettes produced more condensate. The rates of detection of pulmonary tumours also varied between groups (p < 0.01) but this does not necessarily imply that the incidence rates of pulmonary tumours varied. There was no evidence that the detection or incidence rates of any other neoplasms, including malignant lymphoma, were affected by treatment with either of the condensates.

Veterinary medicine and the medical school library

The study of veterinary medicine is becoming increasingly important in the progress of human medicine, and as a consequence the literature of veterinary medicine is assuming increased importance in the libraries of schools of human medicine. In the past decade programs in comparative medicine have been initiated in many centers, reestablishing the linkage between veterinary and human medicine. Since 1966 the National Library of Medicine has assumed extra responsibilities in the collection and control of veterinary medical literature. increased indexing has thus far been the major result, with a resultant increase in the need to consult veterinary journals. Advances in the veterinary curriculum and continued veterinary education have also increased demand for veterinary publications. Such demand must be foreseen and met by medical school libraries if they are to fulfill their obligations to the scholarly medical community.