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.
[Illustration: 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 diarrhoea, 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.