DISINFECTION BY PHYSICAL MEANS.
Natural processes tend to the destruction of pathogenic microbes after their elimination from the patient. Of these desiccation, sunlight, and fresh air are the most potent. Heat and cold have a similar effect. Filtration or mechanical separation deprives a contaminated liquid of its microbes.
Desiccation attenuates the virulence of and finally kills most microbes. In laboratory experiments the vibrio of Asiatic cholera when dried dies in from three hours to two days, according to the degree of desiccation. The bacilli of enteric fever, tuberculosis, and diphtheria only die after drying for a few weeks or even months. The anthrax bacillus may retain its vitality for several years in a desiccated state. Clearly, therefore, desiccation has no administrative value in the prevention of disease, and on the contrary it aids the dissemination of the microbes of tuberculosis, small-pox, scarlet fever, etc.
Direct Sunlight kills a large proportion of the sporeless pathogenic microbes. Diffuse is less energetic in its action than direct sunlight. The bacillus of diphtheria is destroyed by a half to one hour’s exposure to sunlight. As to tubercle bacilli, see page [316]. Downes and Blunt showed that diffused sunlight retards the putrefaction of organic infusions, and that direct sunlight inhibits putrefaction. Sunlight cannot, however, be trusted as an efficient disinfectant. It only secures surface disinfection, and could not be relied upon for pillows, mattresses, etc. M. Ward’s experiments showed that the actinic rays of the sun are germicidal, independent of the heat.
Fresh Air, like sunlight, should be employed as a valuable auxiliary, not as an agent to be depended upon apart from systematic disinfection. The experiments of Downes and Blunt showed that light and oxygen together accomplished what neither alone could do. The presence of air in anthrax increases danger. The anthrax bacillus does not form spores in an animal suffering from this disease, and does not do so post mortem, unless the animal is dissected. Hence the importance of keeping the skin unbroken in this disease, only examining a drop of blood to establish the diagnosis.
Filtration is a means of separating microbes from the gases or liquids containing them. For the filtration of water see page [96]. The carbolic sheet outside a sick-room is supposed to filter the air leaving the room from microbes. It is probably useless except as a reminder to the nurse to change her dress and adopt other precautions on leaving the sick-room.
Settlement of dust also acts as an aerial disinfectant. If a room be locked up, its air next day is almost free from particles, and all that is then required is disinfection of the surfaces of the room and of the articles in it. Whatever method of disinfection is employed, it is not disinfection of the air, but of the surfaces of a room which is the end in view.
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.