Very little information is available regarding reaction (2) but there is little doubt that a direct chlorination of the organic matter does occur and it is more than probable that these chlorinated derivatives are largely responsible for the obnoxious tastes and odours produced in some waters. It has been suggested that these were due to the formation of chloramines. This view was formerly supported by the author but the chloramine treatment at Ottawa and other places has demonstrated the inadequacy of this explanation. It is true that the odour of chloramine is stronger and more pungent than that of chlorine, but chloramine in the Ottawa supply, even with doses as high as 0.5 part per million of available chlorine, has caused no complaints. The odour of some of the organo-chloro compounds is more penetrating and obnoxious than those of chlorine and chloramine, and it is quite possible that some of the higher homologues of chloramine are in this class. It should be noted, however, that some of the chloro-amido compounds prepared by Dakin are white, odourless, crystalline substances. Practically nothing is known regarding the specific nature of the mechanism involved in reaction (3). The hypothesis that chlorine, and chlorine compounds, exert a direct toxic action on the micro-organisms marks an advance in the science of water treatment but does not indicate the physiological processes involved. Cross and Bevan[11] have shown that chloro-amines have a tendency to combine with nitrogenous molecules and to become fixed on cellulose; it is therefore possible that reaction is a cytolytic one in which the chlorine attacks and partially or wholly destroys the membranous envelope of the organisms. A portion of the chlorine or chlorine-compound may also penetrate the membrane and produce changes that result in the death of the organism. BIBLIOGRAPHY [1] Fischer and Proskauer, Rev. d'Hyg., 1884, 6, 515. [2] Warouzoff, Winogradoff, and Kolessnikoff. Russkaia medicina, 1886, Nos. 3 and 32. [3] Race. Jour. Amer. Water Works Assoc., 1918, 5, 63. [4] Griffen and Hedallen. Jour. Soc. Chem. Ind., 1915, 34, 530. [5] Norton and Hsu. Jour. Inf. Dis., 1916, 18, 180. [6] Rideal, S. Jour. Roy. San. Inst., 1910, 31, 33. [7] Dakin, Cohen, Duafresne, and Kenyon. Proc. Roy. Soc., 1916, 89B, 232. [8] Noyes and Lyon. Jour. Amer. Chem. Soc., 1901, 23, 460. [9] Bray and Dowell. Jour. Amer. Chem. Soc., 1917, 39, 905. [10] Jakowkin. Zeit. f. Phys. Chim., 1899, 19, 613. [11] Cross and Bevan. Jour. Soc. Chem. Ind., 1898, 28, 260. [12] Breteau. Jour. Pharm. Chim., 1915, 12, 248. CHAPTER III DOSAGE