It has been shown that infectious diseases are communicated from a sick person to a healthy person by material thrown off from the body of the sick person, the active part of the material being probably some form of living organism. It has been seen that the poisonous material may come off from the patient's body in his breath, in discharges from the mouth and throat, from the skin, from the bowels, and from the kidneys. It is desirable that as soon as possible all poisonous material should be destroyed in one way or another to prevent the spread of the disease. All the means employed to accomplish this are in cluded under the term disinfection, and the materials that may be used for the purpose are called disinfectants.
Disinfectants commonly used are carbolic acid, ch loride of lime,Condy's fl uid (which the pro prietors prepare according to their own method), sulphurous acid, obtained from burning plm, Burnet's fluid (a solution of chloride of zinc), sulphate of copper (blue vitriol) dissolved in water, and sulphate of iron (copperas), sul phuric acid (oil of vitriol), and hydrochloric acid (spirit of salt). These substances ought
to be used in such a way as to destroy the matter of contagion.
There are some substances which, strictly speaking, do not destroy the contagious matter, but simply prevent its growth and multiplication. These are called antiseptics; and a good example is carbolic acid in weak solutions. The living matter of contagion cannot multiply when exposed to the action of an antiseptic, but if the antiseptic be removed the contagion may then go on to multiply. Its growth is merely arrested for the time living organisms are not killed.
is another class of sub stances which may remove the offensive smell of decaying matter without killing or hinder. ing the growth of contagion in it. These are deodorants. It is a true disinfecting action that is wanted, an action which will kill the contagion, so that neither at the moment nor at any future time can it become capable of doing harm.