Mercuric Chloride (HgCl₂, corrosive sublimate) was found by Koch to destroy anthrax bacilli in a dilution of 1 in 20,000. Others have obtained less favourable results, but it is certainly a powerful germicide. The germicidal effect is greatly diminished by contact with organic matter, an insoluble albuminate of mercury being produced. For this reason HgCl₂ is not the best disinfectant for fæces unless mixed with acid, as in the following solution: HgCl₂ ½ oz., HCl 1 oz., aniline blue 5 grains to three gallons of water. This gives a solution of 1 in 960. The colouring is added to avoid accidental poisoning. HgCl₂ is not a good disinfectant for linen. Stains are apt to be fixed by it, and if linen soaked in it is subsequently washed with soap, without first carefully washing out the HgCl₂, it is darkened in colour. It attacks metals, and must not therefore be placed in metal receptacles.
Chloride of Zinc in a solution containing 25 grains to the fluid drachm is known as “Sir William Burnett’s solution.” It is a good deodorant, but an inefficient disinfectant.
Chinosol (C₉H₆NKSO₄) belongs to the quinoline group. It is an almost inodorous powder, very soluble in water, noncorrosive, and does not stain. A solution of 1 in 1200 forms an efficient germicide.
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.