CHAPTER VIII

SUNLIGHT AS A DISINFECTANT

WHAT

has been said in the preceding chapter with reference to the germicidal value of heat and desiccation would indicate the utility of exposing infected articles to sunshine in the open air, as has long been the custom in domestic sanitary practice. But it has been ascertained by carefully conducted experiments that such exposure has an additional value on account of the disinfecting action of the sunlight per se. As long ago as 1877 two English experimenters (Downes and Blunt) in a communication made to the Royal Society of London presented evidence showing that sunlight has an injurious effect upon bacteria, and that sterilisation of cultures in liquid media could be effected by prolonged exposure to direct sunlight. Since then many experiments have been made by different observers and the fact has been fully confirmed. Even the spores of certain bacilli are destroyed by long exposure to sun

light. The distinguished German bacteriologist, Dr. Robert Koch, reported, some years since, the results of his experiments with the tubercle bacillus. He found that the time required to kill this bacillus varies from a few minutes to several hours, depending upon the thickness of the layer exposed. Even diffused daylight exerts a certain germicidal action, although the time of exposure is very much longer-five to seven days for the tubercle bacillus. In the writer's experiments made in 1892 it was found that two hours' exposure to direct sunlight was fatal to the cholera spirillum suspended in a liquid medium.

The electric light, and even gas-light, have also a germicidal action upon certain disease germs, although very much less in degree than sunlight. It has been ascertained that the rays at the violet end of the spectrum have the greatest disinfecting power, while the red rays are comparatively inert.

The facts stated fully sustain the popular idea that the exposure of infected articles of clothing and bedding in the sun is a useful sanitary precaution. Repeated and prolonged exposure will, however, be necessary to ensure safety. In the case of such diseases as smallpox, diphtheria, and scarlet fever more speedy and reliable measures of disinfection will be required. Exposure to the sunlight is nevertheless a

most useful and economical procedure and is to be commended as a routine practice in domestic sanitation, and also as an additional and supplementary precaution when infected articles have been subjected to the action of other disinfectants.

IT

CHAPTER IX

DISINFECTION BY GASES

T is impracticable to disinfect the atmosphere of an occupied apartment; for any gaseous or volatile agent which would destroy disease germs suspended in the air would render it irrespirable. Moreover the air of the sick-room should be constantly renewed by ventilation, and there is far less reason for disinfecting it when the patient has been removed than while it is occupied, for then the air may be quickly renewed by opening doors and windows. As is well known, particles of dust suspended in the air of a room have a tendency to settle upon the floor, upon window ledges, etc., and infected particles from the patient's body will constitute a portion of this dust in such diseases as smallpox and scarlet fever, while in tuberculosis, diphtheria, influenza, and pneumonia expectorated material may become desiccated and constitute a portion of the dust.

Every effort should be made to prevent a room

occupied by patients sick with an infectious disease from becoming infected. Carpets, stuffed furniture, curtains, and other articles difficult to disinfect should be removed at the outset. Indeed, nothing should be left in the room which is not absolutely required, and all furniture and utensils should be of such a character that they can be readily disinfected by washing with boiling water or with a disinfecting solution. Abundant ventilation and scrupulous cleanliness should be maintained, and a disinfecting solution should always be at hand for washing the floor, or articles in use, the moment they are soiled by infectious discharges.

Daily wiping of all surfaces-floors, walls, and furniture-with a cloth wet with a disinfecting solution is to be recommended. For this purpose a solution of chloride of lime (2 per cent.), or of carbolic acid (2 per cent.), or mercuric chloride (1:1000), may be used.

By such precautions the infection of the sick-room may be prevented, especially in those diseases, such as cholera and typhoid fever, in which the infectious agent is not given off from the general surface of the body of the sick person.

If a complete disinfection of the room is required it is indispensable that it be first vacated. It will then be practicable to use certain gaseous disinfectants.