What is allergy?

Sunday, October 4, 2015

   At some time every year, certain people suffer from sneezing, running nose and watery eyes. They suffer from an allergy. It is usually called hay fever. Their bodies react badly to the pollen from plants and grasses that is blown around in the air in early summer. Some people suffer in the autumn, when there is tree pollen about.
   Pollen is not the only thing that can upset allergic people. There are a great many commonplace things like dust and fur that can start allergies. And coughs and sneezes are not the only reactions found in allergies. Rashes and itches are common also.
   The substances that produce allergies are called 'antigens' or 'allergens'. There are many different sorts. They include proteins from bacteria and pollens, and chemical substances from primulas and many other green plants.
   People may also be allergic to foods. Seasonal fruits and vegetables (particularly straw-berries), shellfish, chocolate, eggs and milk are often the cause of food allergies.
   The body reacts to antigens by producing 'antibodies'. A different antibody is produced for each different antigen. When an antibody reacts with an antigen in the blood stream, the antigen is made harmless. However, if the antigen reaches tissue cells before it meets an antibody, it causes irritation in the cells.
   The irritated tissue produces a chemical called 'histamine'. This seems to be responsible for many of the ill-effects of allergies.
   There are many ways of treating allergies. An obvious one is for the sufferer to avoid contact with the substance to which he is allergic. This is often possible if the substance can be identified. It may be that the sufferer will have to avoid contact with the family cat or change his type of pillow if it is feathers that are the root of the trouble.
   One means of identifying what substances a person is allergic to - his allergens - is called the scratch test. Small scratches are made in a row on the person's body. Tiny amounts of various suspected material like pollen and dust are placed in the scratches. If the skin around a particular scratch soon becomes red and swollen then the doctor knows which substance is the culprit.
   Sometimes it is not possible for a sufferer to avoid an allergen. For instance it is not easy to get away from pollen in the air, even in cities. In this case it may be possible to treat the patient by giving him small doses of the allergen, gradually increasing the dosage. The hope is that he will become used to the allergen and not react so badly.
   Another way is to prescribe drugs known as anti-histamines. These combat the histamine which is always released as part of the allergic reaction.
   Antibodies also protect our bodies from attack by bacteria and viruses. They can prevent illnesses such as measles and mumps. Doctors can inject antibodies to immunize people against diseases. They take great care to make sure that these injections do not cause allergy.

Air Conditioning

Sunday, September 20, 2015

   A means of controlling the temperature, moisture, movement and purity of air. Changes in these affect human comfort. They also affect some industrial processes.
   High temperatures and moisture levels are extremely uncomfortable. Invariably they make us feel hot and sticky. They also make it difficult for the body to control its temperature. Usually sweat evaporates and cools the body. If humidity is high, sweat cannot evaporate.
   Man has experimented for centuries with ways of controlling air conditions. There were many ideas, one of the simplest being to hang wet mats over doorways. This cooled the incoming air. But it also moisturized it and that is not always a desirable thing.
   None of the many other systems really did the job. It was not until refrigeration techniques were developed that modern air conditioning standards could be achieved.
Temperature and moisture also affect materials like cloth, paper and certain metals. When printing on paper, or weaving cloth, these air conditions must be kept constant. In the manufacture of delicate instruments, such as those used in spacecraft, conditions must be controlled to protect fine metal parts from rusting and corrosion.
   Air conditioning can be used either to reduce or to increase heat and moisture. However, it is usually concerned with cooling and drying. That is mainly what we will consider in this article.
   In most air conditioning equipment, a refrigeration system is used. A cooling chemical, such as the gas Freon, begins at room temperature. It is condensed by pressure, and this makes it hot. This excess heat is blown away by a fan and the Freon turns into a liquid at room temperature. It is then fed through a fine nozzle into an evaporator where it returns to its gas form. In the course of evaporating it absorbs heat. This process is repeated continually.
    A fan blows air over the evaporator chamber. The air loses heat, which it gives up to the evaporating Freon. It also loses moisture, which condenses on the surface of the chamber. The cooler and drier air is then filtered to remove impurities, such as dust, pollen or smoke, and pumped into the room that is to be air conditioned.
   Most air conditioners can be adjusted to make air hotter and more moist if required.
   The first effective air conditioning machine was invented by Willis H Carrier in 1902. He used it to solve problems that were occurring at a colour printing plant in New York. Paper stretches when it is moist and shrinks when dry. This meant that a sheet could change size between one application of ink and another of a different colour. Thus air conditioning became a necessity rather than a convenience.
   Since then air conditioning has become common in cinemas, public buildings, private homes and even in automobiles.

What is grafting?

Sunday, August 23, 2015

   Imagine an apple tree with bright-red Jonathan apples on one limb, Golden Delicious apples on another, and dark-red Winesaps on a third. It is possible to have just such a tree. The process called grafting makes it possible.

   Grafting means joining parts of two or more plants together so that they grow to be one plant. The top of a young crab apple tree, for example, may be cut off and the twig of another apple tree put in its place. The inner layer of the bark of a woody plant is called the cambium. It is made up of cells that are alive and growing. In grafting, the two cambium layers must come together.

   There are different ways of grafting. The joining is usually protected by a bandage or by a coating of wax.
Fruit trees grown from seeds are not likely to bear fruit just like the fruit that the seeds came from. For the little plant in the seed usually has two different trees as parents. If so, it is sure not to grow into a tree exactly like either parent. The only possible way of getting a new Golden Delicious apple tree is to graft a twig from a Golden Delicious tree on to the stem and roots of some other kind of tree. It may be another apple tree, or a quince tree.

   Grafted trees grow faster and bear sooner than trees raised from seed. The stem and roots already have a good start. Another advantage of grafting is that twigs of trees that are easily hurt by disease can be grafted on trees that are hardier.

   Fruit trees are not the only plants that are grafted. Grapevines, rosebushes, and lilac bushes are a few of the other plants that are often grafted. But only plants with woody stems can be grafted, and the parts must come from plants that are close relatives. It is fun to think of grafting a rose twig on a walnut tree and getting a rosebush 60 feet tall. But roses and walnuts are not close enough relatives to make such a rosebush possible.
Sometimes the top of a grafted plant may be broken off. Then the stem may send out branches and grow into its kind of plant. One man had a funny experience. He grafted twigs of two dwarf catalpa trees to the trunks of two young hardy catalpas. Then he planted the little trees side by side. They grew into very pretty umbrella-shaped trees about ten feet tall. Then a windstorm broke off the top of one tree. Soon the trunk of the damaged tree began to send out branches. It developed into a hardy catalpa nearly 30 feet tall. It and its former twin were a strange pair.