The external causes responsible for disease are due to conditions of weather so severe as to be outside the possibility of self-protection. Excessive heat is responsible each year for deaths from sunstroke, and other conditions of weather are often the direct causes of disease, if not of death.
Accidents are the indirect cause of death, and there will always be a small proportion of the deaths occurring each year due to violence or accident. But, inasmuch as these deaths are clearly preventable, it is the duty of those interested in rural hygiene to study the reasons for accidental death, and, if the number of such accidents can be reduced, to strive for that reduction. As an example, it may be mentioned that each year a number of deaths in New York State, and probably in other states, occur from accidents at culverts and bridges, due to insufficient protection in the way of railings and fences. A method of reducing the deaths from accidents, therefore, would include a proper survey of all the roads of a vicinity to make sure that no danger exists in this regard. Other precautions against preventable accidents will readily suggest themselves.
CHAPTER XV
DISINFECTION
Inasmuch as more than 10 per cent of all deaths are due to bacterial or to various infectious diseases, it is of considerable interest to study the various means by which these germ diseases may be prevented. In this chapter it is proposed to discuss the different ways in which the active agents concerned in the spread of disease may be captured and put to death. It has already been pointed out that infectious diseases can be acquired only by the introduction of the specific germs into the human body, either through the mouth or lungs or through some skin abrasion. Further than this, it is quite as definitely known that the vitality of the germ after leaving a diseased person depends primarily upon its condition at the time of leaving the body and afterwards upon the environment which that germ finds outside of the affected person, while waiting for a chance to make its next human resting place.
It is evident, therefore, that if during the interval which elapses between the time when the germs leave a sick person and the time when they enter another person some method could be found by which these germs could be killed, the progress of the disease would be effectually stopped.
This, in the most general sense, is what is meant by disinfection. It is a determined effort to destroy the carriers of disease while temporarily absent from the human body which is their natural home. This process of killing bacteria, however, is not so simple a matter as it might at first seem. They are, unfortunately, such minute beings that they cannot be seen, so that the warfare is waged against an invisible enemy, not, however, to be despised on that account. The methods of warfare must be uncertain, since the exact location of the enemy cannot be known, and it is manifestly impossible to disinfect the universe. What is done is to fix upon the location or surroundings where the original patient was confined, and, assuming that the germs, if any, which have escaped ready for further infection are somewhere near, to poison the air and the wall and floor of the room in question so that happily the germs may be killed.
Disinfecting agents.