Document X7NOGQXRJM440bJXqyN8BGDqK

176 OCCUPATIONAL TUMORS AND ALLIED DISEASES The occupational carcinogenesis of the skin caused by mineral oil requires a prolonged period of exposure. Southam placed the minimum exposure time of shale oil cancer at rarely less than io years, at which time the precancerous warts make their appearance. Henry (1929), who analyzed large series of cases of mule spinners' cancer for this point, mentioned that the shortest period of exposure observed was 16 years and the longest 63 years j while the maximum incidence occurred after 39 years of contact with the shale oil lubricant. Henry presented his observations on this subject in the following table: EXPOSURE TIME OF MULE SPINNERS' CANCER (Henry) Exposure Time Years 15-19 35-39 40-44 45-49 50-54 55-59 60-64 Percentage of Cases 0.6 18.6 18 15 15.6 8-3 3-o Henry noted that the cancers appeared at a later date than usual, when the exposure either ceased before a neoplasm had appeared or was interrupted for some time. In the following table the distribution of cases upon the various exposure periods is presented, using for the mule spinners' cancers the data given by Bridge and Henry, and a few cases from the literature were added to the list of mineral oil cancers recorded by the same investigators. EXPOSURE TIME OF MINERAL OIL CANCERS (Bridge and Henry) Years ."-15 16-20 21-30 31-40 41-50 51-60 over 60 Total Mule Spinners' Cancers 9 1? 54 107 104 55 6 35^ Other Mineral Oil Cancers 8 4 18 18 840 60 -- -- -- -- -- -- ;--------- -- Total 17 21 72 125 112 59 6 412 It may be emphasized that the above data, in regard to the length of, ex posure time, do not provide any exact information concerning the actual mini mum time of contact necessary for the production of a cancerous response in man. It seems probable that the minimum time is definitely shorter than that listed in the table. This conception seems to be justified because the appearance of oil cancer was delayed, when the exposure was discontinued before the tumor became manifest or when the contact was interrupted for some jime. Oil cancers with a delayed appearance, following a relatively short exposure have been observed in men, who stopped working as mule spinners at an early adult age and drifted into other work. They developed many years later a