CHEMICALS AS DISINFECTANTS AND PRESERVATIVES
231. The prevention of disease epidemics is one of the most striking achievements of modern science. Food, clothing, furniture, and other objects contaminated in any way by disease germs may be disinfected by chemicals or by heat, and widespread infection from persons suffering with a contagious disease may be prevented.
FIG. 160.—Pasteurizing apparatus, an arrangement by which milk is conveniently heated to destroy disease germs.
When disease germs are within the body, the problem is far from simple, because chemicals which would effectively destroy the germs would be fatal to life itself. But when germs are outside the body, as in water or milk, or on clothing, dishes, or furniture, they can be easily killed. One of the best methods of destroying germs is to subject them to intense heat. Contaminated water is made safe by boiling for a few minutes, because the strong heat destroys the disease-producing germs. Scalded or Pasteurized milk saves the lives of scores of babies, because the germs of summer complaint which lurk in poor milk are killed and rendered harmless in the process of scalding. Dishes used by consumptives, and persons suffering from contagious diseases, can be made harmless by thorough washing in thick suds of almost boiling water.
The bedding and clothing of persons suffering with diphtheria, tuberculosis, and other germ diseases should always be boiled and hung to dry in the bright sunlight. Heat and sunshine are two of the best disinfectants.
232. Chemicals. Objects, such as furniture, which cannot be boiled, are disinfected by the use of any one of several chemicals, such as sulphur, carbolic acid, chloride of lime, corrosive sublimate, etc.
One of the simplest methods of disinfecting consists in burning sulphur in a room whose doors, windows, and keyholes have been closed, so that the burning fumes cannot escape, but remain in the room long enough to destroy disease germs. This is probably the most common means of fumigation.
For general purposes, carbolic acid is one of the very best disinfectants, but must be used with caution, as it is a deadly poison except when very dilute.
Chloride of lime when exposed to the air and moisture slowly gives off chlorine, and can be used as a disinfectant because the gas thus set free attacks germs and destroys them. For this reason chloride of lime is an excellent disinfectant of drainpipes. Certain bowel troubles, such as diarrhœa, are due to microbes, and if the waste matter of a person suffering from this or similar diseases is allowed passage through the drainage system, much damage may be done. But a small amount of chloride of lime in the closet bowl will insure disinfection.
233. Personal Disinfection. The hands may gather germs from any substances or objects with which they come in contact; hence the hands should be washed with soap and water, and especially before eating. Physicians who perform operations wash not only their hands, but their instruments, sterilizing the latter by placing them in boiling water for several minutes.
Cuts and wounds allow easy access to the body; a small cut has been known to cause death because of the bacteria which found their way into the open wound and produced disease. In order to destroy any germs which may have entered into the cut from the instrument, it is well to wash out the wound with some mild disinfectant, such as very dilute carbolic acid or hydrogen peroxide, and then to bind the wound with a clean cloth, to prevent later entrance of germs.
234. Chemicals as Food Preservatives. The spoiling of meats and soups, and the souring of milk and preserves, are due to germs which, like those producing disease, can be destroyed by heat and by chemicals.
Milk heated to the boiling point does not sour readily, and successful canning consists in cooking fruits and vegetables until all the germs are killed, and then sealing the cans so that germs from outside cannot find entrance and undo the work of the canner.
Some dealers and manufacturers have learned that certain chemicals will act as food preservatives, and hence they have replaced the safe method of careful canning by the quicker and simpler plan of adding chemicals to food. Catchup, sauces, and jellies are now frequently preserved in this way. But the chemicals which destroy bacteria frequently injure the consumer as well. And so much harm has been done by food preservatives that the pure food laws require that cans and bottles contain a labeled statement of the kind and quantity of chemicals used.
Even milk is not exempt, but is doctored to prevent souring, the preservative most generally used by milk dealers being formaldehyde. The vast quantity of milk consumed by young and old, sick and well, makes the use of formaldehyde a serious menace to health, because no constitution can endure the injury done by the constant use of preservatives.
The most popular and widely used preservatives of meats are borax and boric acid. These chemicals not only arrest decay, but partially restore to old and bad meat the appearance of freshness; in this way unscrupulous dealers are able to sell to the public in one form or other meats which may have undergone partial decomposition; sausage frequently contains partially decomposed meat, restored as it were by chemicals.
In jams and catchups there is abundant opportunity for preservatives; badly or partially decayed fruits are sometimes disinfected and used as the basis of foods sold by so-called good dealers. Benzoate of soda, and salicylic acid are the chemicals most widely employed for this purpose, with coal-tar dyes to simulate the natural color of the fruit.
Many of the cheap candies sold by street venders are not fit for consumption, since they are not only made of bad material, but are frequently in addition given a light dipping in varnish as a protection against the decaying influences of the atmosphere.
The only wise preservatives are those long known and employed by our ancestors; salt, vinegar, and spices are all food preservatives, but they are at the same time substances which in small amounts are not injurious to the body. Smoked herring and salted mackerel are chemically preserved foods, but they are none the less safe and digestible.
235. The Preservation of Wood and Metal. The decaying of wood and the rusting of metal are due to the action of air and moisture. When wood and metal are surrounded with a covering which neither air nor moisture can penetrate, decay and rust are prevented. Paint affords such a protective covering. The main constituent of paint is a compound of white lead or other metallic substance; this is mixed with linseed oil or its equivalent in order that it may be spread over wood and metal in a thin, even coating. After the mixture has been applied, it hardens and forms a tough skin fairly impervious to weathering. For the sake of ornamentation, various colored pigments are added to the paint and give variety of effect.
Railroad ties and street paving blocks are ordinarily protected by oil rather than paint. Wood is soaked in creosote oil until it becomes thoroughly saturated with the oily substance. The pores of the wood are thus closed to the entrance of air and moisture, and decay is avoided. Wood treated in this way is very durable. Creosote is poisonous to insects and many small animals, and thus acts as a preservation not only against the elements but against animal life as well.