The haloid compounds of fluorine, chlorine, bromine, and iodine all possess specific germicidal properties. They depend for their action on the presence of the freed haloid substance.

Fluorine is too active a substance to be handled, and only in exceptional cases are bromine-liberating compounds applicable. The halogens are only useful in the presence of a certain amount of moisture. A 2 per cent. solution of chlorine water is capable of acting on the anthrax bacillus spores in 15 seconds, and in proportions of 1: 700 it will completely prevent the development of this micro-organism. The disinfecting power of the chlorine-containing compounds is much enhanced if nascent chlorine is being formed. Chlorinated lime is a useful disinfectant for house purposes. Typhoid urine is well disinfected if the chlorinated lime is present in solution 1: 500 to 1: 1000 in five minutes. In the stools, the presence of albuminous material and salts makes it imperative to use this disinfectant as strong as 1 to 2 per cent. and have it act at least ten minutes.

Iodine used locally is a powerful germicide and it may also be used internally.

Iodine in combination with various aromatic or fatty bodies may be discussed here to advantage. The most characteristic of these bodies is iodoform. It is necessary that these bodies should liberate free iodine to be active germicides.