THE SUN AS A DISINFECTANT.
By G. M. Sternberg
[Surgeon-General G. M. Sternberg, U. S. A., in Youth’s Companion.] ALTHO man from the earliest times has recognized that the radiations of the sun—light and heat—are essential for the continuance of life upon our planet, only within the last twenty years has it been demonstrated that sunlight is fatal to some of the lower forms of living things, including certain disease germs which are the cause of some of the most fatal infectious diseases that afflict the human race. In fact, the greatest disinfectant in nature is light, or, to be more exact, the radiations of the sun, including heat rays, light rays, and the invisible rays at the violet end of the solar spectrum. An infectious disease is one which may be contracted by the introduction into the living body of living disease germs, which may be contained in different kinds of infectious material. Thus the disease germ (bacillus) which produces diphtheria is contained in the “exudate” or “false membrane” deposited in the throat or nasal passages of those suffering from this disease; and the material coughed up by a patient with diphtheria is infectious material. In cases of pulmonary consumption, the germ (also a bacillus) is contained in material coughed up from the lungs—sputa. In cholera and typhoid fever the discharges from the bowels contain the germ, and are consequently infectious material. In smallpox and scarlet fever the germ is present in material detached from the general surface of the body. Now the object of disinfection is to prevent the extension of infectious disease by destroying the specific infectious agents—germs—which give rise to them; and this is accomplished by the use of disinfectants. Having, as I hope, made this clear, I desire to call attention to the fact that the term disinfectant is popularly used in a much broader sense. Any chemical agent which destroys or masks bad odors is commonly spoken of as a disinfectant, and there are a large number of so-called “disinfectants” in the market which are simply deodorants, and which are entirely untrustworthy for the destruction of infectious material—that is, of material containing living disease germs. These disease germs belong to the class of low vegetable organisms—microscopic plants—known as bacteria, which, as a rule, thrive better in the darkness than when exposed to daylight; and some of them are quickly destroyed by exposure to direct sunlight. In experiments made by me in 1893 it was demonstrated that the cholera bacillus is infallibly killed by exposure to direct sunlight for an hour or two; and the distinguished German bacteriologist, Dr. Robert Koch, has shown that the bacillus of consumption—tubercle bacillus—is destroyed by similar exposure in a time varying from a few minutes to several hours—depending upon the thickness of the layer of material in which it is embedded. As a result of this, it is evident that the material coughed up by patients with consumption, and containing tubercle bacilli in vast numbers, is far less dangerous to the community in regions where the patient can live out of doors, and where the sun shines every day in the year, as is the case in portions of Colorado, New Mexico, Arizona, and California, than in sections of the country where climatic conditions are unfavorable to an outdoor life, and where the skies are clouded a considerable part of the time. I may be permitted, also, to call attention to the favorable influence of an outdoor life in an elevated and dry region, where the sun is rarely obscured by clouds, upon patients suffering from pulmonary consumption, especially in its early stages. Some disease germs, which are not killed outright by exposure to the sun’s rays, are greatly restrained in their development. This is true of the bacillus of typhoid fever. Altho it has been shown by carefully conducted experiments that certain disease germs are promptly destroyed by the luminous radiations from the sun, and especially by those at the violet end of the solar spectrum, it is also true that the heat rays play an important part in the destruction of harmful bacteria. This is partly due to the fact that certain disease germs are quickly destroyed by being deprived of all moisture—by desiccation. Thus the germs of cholera and of pneumonia quickly perish when completely dried. Other germs, however, as those of typhoid fever, of diphtheria, and of consumption, may retain their vitality in a dried condition for several months. But the germs of all these diseases are destroyed by a comparatively low temperature. In experiments which I made several years ago, I ascertained that the germs of pneumonia and of cholera were killed by exposure for a few minutes to a temperature of one hundred and twenty-six degrees Fahrenheit. A still lower temperature is effective if the time of exposure is prolonged. It is, therefore, evident that prolonged exposure to the direct rays of the sun would destroy these germs, independently of the disinfecting power or germicidal action of the luminous rays, or the fatal results of desiccation. Other disease germs require a higher temperature for their destruction. The typhoid bacillus and the bacillus of diphtheria are killed by exposure to a temperature of one hundred and forty degrees Fahrenheit for ten minutes. In general, it may be stated that this temperature is fatal to all the most important disease germs, with the exception of the tubercle bacillus, which requires a somewhat higher temperature. The facts stated furnish a scientific basis for practical disinfection, and it is evident that when sunshine is available no chemical agents are essential for the destruction of disease germs. Any article of food or drink which has been heated for a few minutes to something near the boiling point of water is absolutely safe so far as any danger from disease germs is concerned; and any article of clothing which has been put through the ordinary operations of the laundry is as safe as if it had been placed for an hour in an expensive steam disinfector or immersed in a strong disinfecting solution. It will be seen that scientific investigations fully justify the practice of good housewives, who at frequent intervals expose their blankets and articles of woolen clothing which can not be placed in boiling water without injury, to a prolonged sun-bath; who scald out milk-pans and kitchen utensils, and place them in the sun to dry; and who open up their sleeping apartments for the admission of sunlight and fresh air. The fresh air displaces the air which has been confined in the room, and sweeps out into the sunlight many disease germs which may be suspended in it. How Infectious Diseases May Travel.
No doubt it is largely due to the disinfecting power of the sun’s rays that infectious diseases are rarely, if ever, conveyed any considerable distance through the air. A case of smallpox or of diphtheria or of typhoid fever across the street does not place the occupants of neighboring houses in any special danger, so far as the transmission of these infectious diseases through the air is concerned. But there are other ways in which disease germs may be carried, and by which they are usually conveyed from the sick room to other and often to distant localities. They may be carried in clothing sent out of the house for laundry, or they may be attached to the clothing of those who have visited the sick-room, or may adhere to the hair of pet animals, or to the feet of that domestic pest, the house-fly, which is now supposed to be responsible for the occurrence of many cases of infectious disease, the origin of which could not be traced. One very common and widely distributed infectious disease is carried through the air for considerable distances, but in this case the germ does not travel independently, and is not exposed to the dangers of being killed by sunlight and desiccation. It is carried in the body of an “intermediate host,” the mosquito. The disease is malarial fever, which has been proved to be due to a blood parasite that is introduced into the human body by means of the puncture made by infected mosquitoes. It is well to remember that the best disinfectant is that supplied by nature—the light and heat which travel ninety million of miles from the great central star of our planetary system, to irradiate the earth and make it fruitful and habitable for man.