Washing is the most efficacious means of removing infection. It is a mechanical means of removing the particular matter of which the contagium consists from the person or article to which it adheres into the water, which subsequently enters the drain, in the same way as do urine and fæces. Washing is an absolutely efficient means of purifying articles that can be completely submitted to it. A consideration of the physical laws governing the spread of infection will make this clear. The contagia are passive. When contained in a liquid they cannot escape from it under ordinary circumstances. Thus foul smelling gases may escape from sewage, but bacteria do not escape, except rarely during bubbling, or from dried portions of the invert of the sewer. Barring rare accidents “microbes submerged are imprisoned.” Contagia are harmless until they become dust. Hence the danger associated with the use of pocket handkerchiefs in such diseases as influenza and phthisis; and the importance of keeping all infectious discharges wet, until they can be finally disposed of.

DISINFECTION BY HEAT.

Heat may be applied in various ways: (1) Prolonged boiling in water of materials which are not spoilt by this means. (2) Destruction by fire of infected articles. (3) Dry hot air. (4) Steam.

Boiling kills most pathogenic microbes. The cholera vibrio is killed in four minutes at a temperature of 52° C. (126° F.); the typhoid bacillus at 59°.4 C. (138°.8 F.) in ten minutes. If boiling be continued for five minutes, the spores of pathogenic microbes are killed. The addition of one to two per cent. of washing soda to the water hastens this effect. For infected linen nothing beyond this is required.

Destruction by Fire is to be recommended for comparatively worthless articles, such as toys, straw from beds, rags, old clothing and bedding.

Dry Hot Air has been largely used in the past in ovens, for the disinfection of bulky bedding. It is now entirely superseded by steam. Its disadvantages are that (a) heat penetrates very slowly into the interior of bedding. Disinfection in test experiments was not accomplished in the interior of small bundles of clothes in three or four hours. (b) Scorching of articles often occurs. The sole advantage of this method is that bound books and leather goods are less liable to be damaged by it than by steam. If no other apparatus is available a baker’s oven will serve to kill the non-sporiferous microbes of cholera, enteric fever, and diphtheria, as well as animal vermin. If, however, we accept the proper test proposed by Buchanan of the efficacy of disinfection, the “destruction of the most stable known infective matter,” dry heat is unsatisfactory.

Steam may be employed as a disinfectant either (a) superheated, or (b) saturated, i.e. close to the temperature at which condensation occurs. This temperature depends upon the pressure under which the water has been boiled. At ordinary atmospheric pressure it is 100° C. (212° F.). The temperature of boiling is raised by subjecting the water to pressure. Consequently boiling water and the steam produced from it may be at any temperature. Thus steam may be

Fig. 57.
Equifex Saturated Steam Disinfector.