---------------+---------------+-------------+-------------+------------- | Morphology | Spore | Gelatine | Reaction in | | Formation |Liquefaction | Litmus Milk +--------+------+------+------+------+------+------+------ |Bacilli.|Cocci.| Pos. | Neg. | Pos. | Neg. | Pos. | Neg. ---------------+--------+------+------+------+------+------+------+------ No. of strains | 100 | 5 | 89 | 16 | 68 | 37 | 98 | 7 Per cent. | 95.2 | 4.7 | 84.7 | 15.2 | 64.7 | 35.2 | 93.3 | 6.6 ===============+========+======+======+======+======+======+======+====== | Indol | Acid | Reduction | Inhibition | Production | Production | of | by Gentian | | in Glucose | Nitrates | Violet +--------+------+------+------+------+------+------+------ | Pos. | Neg. | Pos. | Neg. | Pos. | Neg. | Pos. | Neg. ---------------+--------+------+------+------+------+------+------+------ No. of strains | 75 | 30 | 61 | 44 | 40 | 65 | 98 | 7 Per cent. | 71.4 | 28.5 | 58 | 41.9 | 38 | 61.9 | 93.3 | 6.6 ---------------+--------+------+------+------+------+------+------+------ The removal of intestinal forms is, of course, merely a relative one and when large quantities of treated water are tested their presence can be detected. The author, in 1915, made a number of experiments to ascertain whether the _B. coli_ found after chlorination were more resistant to chlorine than the original culture. The strains surviving treatment with comparatively large doses were fished into lactose broth and subjected to a second treatment, the process being repeated several times. The velocity of the germicidal reaction with the strains varied somewhat, but not always in the same direction, and the variations were not greater than were found in control experiments on the original culture. No evidence was obtained that the surviving strains were in any way more resistant to chlorine than the original strain; in considering the results it should be borne in mind that the surviving strains were cultivated twice on media free from chlorine before again being subjected to chlorination. A number of the strains that survived several treatments were cultivated in lactose broth and the acidity determined quantitatively. All the cultures produced less acid than the original culture, and the average was materially less than the original. These results point to a diminution of the bio-chemical activity by action of the chlorine.