Collis[6] estimated the attack rate in lead-smelting works at 30, and in spelter works at 10, per 1,000 per annum. In one factory he found it 80 per 1,000, and in a spelter works five cases occurred in a few months among seven workers. The distribution of the reported cases from year to year was as follows: +--------------+-----+-----+-----+-----+-----+-----+-----+ | Process. |1900.|1901.|1902.|1903.|1904.|1905.|1906.| +--------------+-----+-----+-----+-----+-----+-----+-----+ |Lead smelting | 21 | 26 | 13 | 13 | 7 | 10 | 16 | |Desilverizing | 1 | 3 | 9 | 10 | 16 | 6 | 9 | |Spelter | 5 | 11 | 3 | 4 | 4 | 5 | 9 | |Other (copper,| 7 | 14 | 3 | 10 | 6 | 3 | 4 | |iron, etc.) | | | | | | | | | +-----+-----+-----+-----+-----+-----+-----+ | | 34 | 54 | 28 | 37 | 33 | 24 | 38 | +--------------+-----+-----+-----+-----+-----+-----+-----+ +--------------+-----+-----+-----+-----+-----+------+ | Process. |1907.|1908.|1909.|1910.|1911.|Total.| +--------------+-----+-----+-----+-----+-----+------+ |Lead smelting | 21 | 31 | 28 | 21 | 33 | 240 | |Desilverizing | 4 | 3 | 6 | -- | 3 | 70 | |Spelter | 2 | 31 | 25 | 12 | 11 | 122 | |Other (copper,| 1 | 5 | 7 | 1 | 1 | 62 | |iron, etc.) | | | | | | | | +-----+-----+-----+-----+-----+------+ | | 28 | 70 | 66 | 34 | 48 | 494 | +--------------+-----+-----+-----+-----+-----+------+